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. Drain.
Stir in tomato sauce, Velveeta, mustard (I could not get much mustard flavor with the ground mustard, so I added a squeeze of prepared mustard), Worcestershire sauce, salt and pepper to taste until cheese is melted, 4-6 minutes.
Transfer to a greased 13x9-in. or 3-1/2-qt. baking dish. Sprinkle with 1 1/2 cup cheddar cheese and bacon. Top with Tater Tots. Bake, uncovered, 30 minutes; top with remaining 1/2 cup cheese and bake additional 10 minutes. Top with tomatoes, pickles and remaining onion. **I have tomato haters, so instead of tomatoes,I drizzled a little ketchup on top. Yield: 12 servings.