Spray an 11 x 16 oven-safe dish with nonstick spray or coat with coconut oil
In a small bowl, mix all seasoning ingredients together.
Place sliced peppers, chopped onions and diced tomatoes into the oven-safe dish and coat with half of the seasoning mix.
Coat chicken with remaining half of seasoning mix.
Place the seasoned chicken on top of the vegetables in the dish. Season everything with salt and pepper, if desired.
Bake in oven for 25-30 minutes. Check that the chicken is cooked (165F) at the end, since oven time may vary. If desired, add cheese at the end and return to oven for 5 more minutes, or until cheese is melted.