Preheat oven to 400 degrees and coat a 13x9 baking dish with cooking spray. Over medium-high cook the bacon or cook in oven on a baking rack for about 15 minutes. In a large skillet, cook the ground beef and onion until completely browned and the onions are soft. Stir in ketchup and mustard and spread mixture into baking dish.
Sprinkle with crumbled bacon, then cheese.
Top with tater tots. Bake for about 20-25 minutes or until potatoes are golden brown and mixture in heated through.