Preheat oven to 400°. Spray a baking dish or use a preseasoned cast iron skillet.
Cut each chicken breast in half but not all the way through, butterfly style.
In a medium bowl place in olive oil, salt, pepper, garlic powder, oregano, and basil and mix to make a paste. Rub into the outsides of each chicken breast.
Pour one-half of the marinara into the bottom of the baking dish.
Take each chicken breast and fill it with mozzarella, and 4 or 5 pepperoni slices. Then close the chicken breast and place in baking dish on top of marinara sauce.
Spoon remaining marinara over the chicken. Then top with shredded cheese, grated parmesan cheese, and pepperonis.
Bake for 25 - 30 minutes or until the internal temperature on the chicken reads 165°.