As either a hearty party sandwich or a filling lunch or dinner, this sub will rise to the top of your list of favorites. It's also a perfect contribution to a potluck...but don't expect to have any leftovers!
In a large bowl, combine the eggs, milk, onion, garlic, bread crumbs, salt and Italian seasoning. Crumble sausage and beef over mixture; mix well. Shape into 1-in. balls. Place in a greased 13-in. x 9-in. x 2-in. baking dish. Bake at 425° for 15 minutes or until browned.
In a Dutch oven, heat the spaghetti sauce over medium heat. Add meatballs; simmer for 15 minutes. Meanwhile, bake bread at 325° for 10 minutes or until heated through. Place mozzarella cheese on bottom half of bread; spoon meatballs onto cheese. Replace top. Slice sandwich into serving-size portions; serve with extra spaghetti sauce and Parmesan cheese if desired.