Preheat the oven to 350F. In a large bowl, combine 1/3 cup of the spaghetti sauce, the bread crumbs, onion, cheese, egg, parsley, and garlic powder; mix well. Add the ground beef to the mixture; mix well. Shape into about sixteen 2-inch meatballs and arrange in a 9" x 13" baking pan. Bake for 20 minutes. Remove from the oven and drain the liquid. Pour the remaining sauce over the meatballs and return to the oven for 10 to 15 minutes more, or until hot and fully cooked. Serve on the sandwich rolls.