In a bowl, combine 1/4 cup mozzarella, ricotta, Parmesan, Italian seasoning, garlic powder, salt and pepper; set aside. Cut loaf of bread in half lengthwise. Cut a 2 inch wide strip down the center of each half to within an inch of the bottom of the bread. Remove cut portion and save for another use. If desired, toast the bread halves under the broiler until lightly browned.
Spread the cut side of the bread with cheese mixture. Place six meatballs in each half; top with spaghetti sauce. Place on baking sheet. Bake at 400 F for 20-25 minutes or until heated through. Sprinkle with remaining mozzarella cheese. Cut into slices; top with pepper rings, if desired.