Preheat your oven to 375°F and lightly grease a 9x13-inch baking dish.
Cook the ground beef in a large skillet over medium heat until no longer pink, breaking it into crumbles as it cooks (about 5-7 minutes).
Add diced onion and chopped bell pepper to the skillet. Cook for 5 minutes until softened, then stir in the minced garlic for the final minute.
Stir in the tomato sauce, Worcestershire sauce, mustard, brown sugar, salt, and pepper. Let the mixture simmer for 5 minutes, allowing the flavors to meld together.
Spread the beef mixture evenly in the prepared baking dish. Sprinkle 1 cup of shredded cheddar cheese over the top.
Arrange the frozen tater tots in an even layer over the cheese. Bake for 25-30 minutes, or until the tater tots are crispy and golden brown.
Remove the casserole from the oven and top with the remaining cup of cheddar cheese. Return to the oven for an additional 5 minutes until the cheese is melted and bubbly.
Allow the dish to cool for a few minutes before serving. Enjoy with a side salad or steamed veggies for a complete meal.