Heat butter in large pan to 350 F, place chicken, onion, garlic and peppers in and let sizzle for 30 seconds.
Flip chicken, let cook 20 seconds, separate slices and mix in onion/garlic/peppers.
Cook chicken to 165 degrees F, add pesto, tomatoes and cheese then stir over low heat until cheese is melted.
Toss Spinach and place in split roll. Add the chicken/cheese mixture and serve.