Preheat oven to 400°. In a large skillet over medium heat, cook beef and 1 cup onion, crumbling meat, until beef is no longer pink and onion is tender, 6-8 minutes; crumble meat; drain. Stir in tomato sauce, Velveeta, mustard and Worcestershire sauce until cheese is melted, 4-6 minutes., Transfer to a greased 13x9-in. or 3-1/2-qt. baking dish. Sprinkle with cheddar cheese and bacon. Top with Tater Tots. Bake, uncovered, 35-40 minutes or until bubbly. Top with tomatoes, pickles and remaining onion.