01 - Preheat oven to 375°F. In a large skillet over medium heat, cook ground beef and chopped onion until the beef is browned and onions are softened. Drain excess fat.
02 - Stir ketchup, mustard, salt, and pepper into the beef mixture. Spread the mixture in an even layer in a baking dish.
03 - Arrange frozen tater tots in a single layer on top of the beef mixture. Sprinkle shredded cheddar cheese evenly over the tater tots.
04 - Bake for 25 to 30 minutes, or until the tater tots are crispy and golden and the cheese is melted and bubbling.