Combine The Ground Beef And Italian Sausage In A Large Heavy Skillet. Cook Over Medium Heat Until Evenly Browned. Drain Off Excess Grease, And Season Meat With Italian Seasoning. Heat The Pasta Sauce In A Saucepan Over Medium Heat Until Heated Through. When The Sauce Is Warm, Stir In The Sugar. Fill Taco Shells With The Meat Mixture, Spoon Pasta Sauce Over, And Top With Mozzarella Cheese.