Preheat oven to 425ºF. Lightly spray a 9x13-inch pan with cooking spray.
Place chicken in the baking dish. Sprinkle with ranch seasoning and au jus gravy mix.
Top the chicken with pepperoncini peppers and top wtih butter slices.
Bake chicken for 25 to 30 minutes, until chicken reaches an internal temperature of 165ºF.
