This phase II trial studies how well stereotactic body radiation therapy with or without nivolumab works in treating patients with stage I-IIA non-small cell lung cancer or cancer that has come back. Stereotactic body radiation therapy uses special equipment to position a patient and deliver radiation to tumors with high precision. This method can kill tumor cells with fewer doses over a shorter period and cause less damage to normal tissue. Immunotherapy with monoclonal antibodies, such as nivolumab, may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread. Giving stereotactic body radiation therapy and nivolumab may work better at treating non-small cell lung cancer.