Combine beef, 2 tbs tomato sauce, onion, egg, bread crumbs and salt; shape into 1-inch meatballs. In skillet lightly brown meatballs.; drain fat. Stir in rest of tomato sauce, mixed vegetables, thyme and pepper; simmer 5 minutes. Meanwhile, press potatoes over bottom of baking dish; drizzle with oil and place under broiler until lightly browned. Spoon meatball mixture over; arrange cheese strips in lattice pattern on top. Bake at 375 degrees for 25 minutes.