Preheat oven to 350 degrees.
Butterfly thawed chicken. Coat chicken with olive oil, season to liking with seasoned salt and pepper or any other seasoning you prefer. Place chicken breasts in glass baking dish.
Chop 1/4 cup onion and 40 pepperoni. Mix with one can chilies. Sauté on high in olive oil on small skillet. Fill chicken with sautéed mixture. Put the second can of chilies on top of chicken.
Cook for 20-30 minutes until chicken is done.