Step 1: Preheat your oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish.
Step 2: Heat olive oil in a large skillet or Dutch oven over medium-high heat. Add the ground beef, breaking it apart with a spoon. Cook until thoroughly browned, about 5-7 minutes. Drain any excess grease.
Step 3: Add the chopped onion and bell pepper (if using) to the skillet with the beef. Cook for 5-7 minutes, until softened. Stir in the minced garlic and cook for another minute until fragrant.
Step 4: Stir in the tomato sauce, ketchup, brown sugar, yellow mustard, and Worcestershire sauce. Bring the mixture to a simmer, then reduce heat to low and let it cook for 5-10 minutes, allowing the flavors to meld and the sauce to thicken slightly. Season with salt and pepper to taste.
Step 5: Spread the sloppy joe mixture evenly into the prepared baking dish.
Step 6: Sprinkle the shredded cheddar cheese evenly over the sloppy joe mixture.
Step 7: Arrange the frozen tater tots in a single layer over the cheese. For extra crispy tots, you can lightly spray them with cooking spray.
Step 8: Bake for 30-35 minutes, or until the casserole is bubbly around the edges and the tater tots are golden brown and crispy. Let stand for a few minutes before serving.