In a bowl, combine onions, crumbs and Parmesan cheese. Add beef and mix well. Shape into 1-inch balls; place on a rack in a shallow baking pan. Bake at 400º for 15-20 minutes or until no longer pink. Meanwhile, arrange bread in a single layer in an ungreased 13x9 baking dish. Combine cream cheese, mayonnaise, Italian seasoning and pepper; spread over the bread. Sprinkle with 1/2 cup Mozzarella. Combine sauce, water and garlic; add meatballs. Pour over cheese mixture; sprinkle with remaining mozzarella. Bake, uncovered, at 350º for 30 minutes or until heated through. Note: Do not use light or fat-free mayonnaise.