Pound chicken breasts flat with a meat mallet. Season to taste with garlic powder, salt, pepper and Italian style seasoning.
Place 4 to 5 slices pepperoni on each breast and top each with a slice of cheese. Roll up breasts and fasten with toothpicks.
Fry the chopped pepperoni in a medium skillet until it has released most of its oil. Remove pepperoni from skillet and set aside. Brown chicken rolls in pepperoni oil about 5 to 10 minutes each side. Place chicken in a baking dish. Combine spaghetti sauce and chopped pepperoni and pour over chicken.