Inclusion Criteria:

          -  Provision of signed informed consent prior to any screening procedures being performed

          -  Histologically (or cytologically) confirmed diagnosis of adenocarcinoma of the colon
             or rectum, with clinical confirmation of unresectable and/or metastatic disease that
             is measurable according to Response Evaluation Criteria in Solid Tumors (RECIST) 1.1
             criteria

          -  Confirmation of BRAFV600E tumor as detected by a Clinical Laboratory Improvement
             Amendments (CLIA)-certified laboratory

          -  Confirmation of microsatellite stable (MSS) status in a CLIA-certified laboratory

          -  Prior treatment with at least one, but no more than two, systemic chemotherapy
             regimen(s) for mCRC, or recurrence/progression with development of unresectable or
             metastatic disease within 6 months of adjuvant chemotherapy for resected colorectal
             cancer

          -  Eastern Cooperative Oncology Group (ECOG) performance status =< to 1

          -  Absolute neutrophil count (ANC) >= 1.0 x 10^9/L

          -  Hemoglobin (Hgb) >= 9 g/dL with or without transfusions

          -  Platelets (PLT) >= 100 x 10^9/L without transfusions

          -  Aspartate aminotransferase (AST) and/or alanine aminotransferase (ALT) =< 2.5 x upper
             limit of normal (ULN)

          -  Total bilirubin =< to 1.5 x ULN and < 2 mg/dL

               -  Note: Patients who have a total bilirubin level > 1.5 x ULN will be allowed if
                  their indirect bilirubin level is =< 1.5 x ULN

          -  Serum creatinine =< 1.5 x ULN, or calculated creatinine clearance (determined as per
             Cockcroft-Gault) >= 50 mL/min at screening

          -  Corrected QT (QTc) interval =< 480 ms (preferably the mean) from triplicate
             electrocardiograms (ECGs)

          -  Able to take oral medications

          -  Female patients are either postmenopausal for at least 1 year, are surgically sterile
             for at least 6 weeks, or must agree to take appropriate precautions to avoid pregnancy
             from screening through follow-up if of childbearing potential. Note: Permitted
             contraception methods should be communicated to the patients and their understanding
             confirmed. For all females, the pregnancy test result must be negative within 24 hours
             of starting treatment with nivolumab. Males to avoid fathering a child from screening
             through 100 days following the end of therapy

        Exclusion Criteria:

          -  Concurrent corticosteroid therapy or concurrent use of any other immunosuppressive
             medication (corticosteroid use on study as a pre-medication for IV contrast
             allergies/reactions is allowed). Subjects who are receiving daily steroid replacement
             therapy (the equivalent of prednisone =< 10 mg daily) serve as an exception to this
             rule

          -  Prior treatment with a BRAF inhibitor, MEK inhibitor, or ERK inhibitor (of note,
             regorafenib is not considered a BRAF inhibitor for the context of eligibility
             criteria)

          -  Prior treatment with anti-EGFR therapies

          -  Prior immune checkpoint therapy including, but not limited to, an anti-PD-1,
             anti-PD-L1, anti-PD-L2, anti-CD137, or anti-cytotoxic T-lymphocyte-associated
             antigen-4 (CTLA-4) antibody, or any other prior immune-modulating agent administered
             with antineoplastic intent (monoclonal antibodies used against VEGF are permitted)

          -  Prior allogeneic tissue/solid organ transplant

          -  History of (non-infectious) pneumonitis that has required oral or IV steroids

          -  Receipt of a live vaccine within 30 days prior to the first administration of study
             medication. Seasonal flu vaccines that do not contain a live virus are permitted

          -  History of a grade 3 or 4 allergic reaction attributed to humanized or human
             monoclonal antibody therapy

          -  Active infection requiring concurrent antibiotic use

          -  Any symptomatic brain metastasis. Note: Patients previously treated or untreated for
             this condition who are asymptomatic in the absence of corticosteroid and
             anti-epileptic therapy are allowed. Brain metastases must be stable for > or equal to
             4 weeks, with imaging (e.g., magnetic resonance imaging [MRI] or computed tomography
             [CT]) demonstrating no current evidence of progressive brain metastases at screening

          -  Leptomeningeal disease

          -  Previous or concurrent malignancy within 3 years of study entry, with the following
             exceptions: adequately treated basal or squamous cell skin cancer, superficial bladder
             cancer, prostate intraepithelial neoplasm, carcinoma in-situ of the cervix, or other
             noninvasive or indolent malignancy; other solid tumors treated curatively without
             evidence of recurrence for at least 3 years prior to study entry

          -  History of acute coronary syndromes (including myocardial infarction, unstable angina,
             coronary artery bypass grafting, coronary angioplasty, or stenting) < 6 months prior
             to screening, symptomatic chronic heart failure (i.e. grade 2 or higher), history or
             current evidence of clinically significant cardiac arrhythmia and/or conduction
             abnormality < 6 months prior to screening except atrial fibrillation and paroxysmal
             supraventricular tachycardia

          -  Uncontrolled hypertension defined as persistent elevation of systolic blood pressure
             >= 170 mmHg or diastolic blood pressure >= 100 mm Hg, despite current therapy

          -  Known positive serology for HIV (human immunodeficiency virus), active hepatitis B,
             and/or active hepatitis C infection

          -  Known history of acute or chronic pancreatitis (history of acute pancreatitis with no
             recurrent events in the prior 24 months are permitted)

          -  Patients with a history of inflammatory bowel disease, including ulcerative colitis
             and Crohn's disease, are excluded from this study, as are patients with a history of
             symptomatic autoimmune disease (e.g., rheumatoid arthritis, systemic progressive
             sclerosis [scleroderma], systemic lupus erythematosus, autoimmune vasculitis [e.g.,
             Wegener's granulomatosis]); central nervous system (CNS) or motor neuropathy
             considered of autoimmune origin (e.g., Guillain-Barre syndrome and myasthenia gravis,
             multiple sclerosis). Patients with Graves' disease will be allowed

          -  Impaired gastrointestinal function or disease that may significantly alter the
             absorption of study drug (e.g., ulcerative diseases, uncontrolled vomiting,
             malabsorption syndrome, small bowel resection with decreased intestinal absorption)

          -  Any other condition that would, in the investigator's judgment, contraindicate the
             patient's participation in the clinical study due to safety concerns or compliance
             with clinical study procedures

          -  Major surgery =< 6 weeks prior to starting study drug or failure to recover from side
             effects of such procedure at the discretion of the treating investigator

          -  Pregnant or nursing (lactating) women, where pregnancy is defined as the state of a
             female after conception and until the termination of gestation, confirmed by a
             positive human chorionic gonadotropin (hCG) laboratory test

          -  Medical, psychiatric, cognitive or other conditions, according to investigator
             judgment, that may compromise the patient's ability to understand the patient
             information, give informed consent, comply with the study protocol or complete the
             study