In a large mixing bowl combine beef, sausage, bread crumbs, Parmesan, garlic, egg, parsley, oregano, salt and pepper by hand.
Form into 16 meatballs approximately 1 1/2-inch in diameter (can be made a day ahead, stored in refrigerator). Coat bottom of a 9 x 12-inch baking dish with tomato sauce and line with meatballs.
Bake uncovered for 20 minutes. Turn each meatball upside down and bake an additional 10-15 minutes. Use an instant read thermometer to confirm meatballs are fully cooked. (160° F internal temperature)