Preheat the oven to 350°F/180°C and grease a 9×13 inch casserole dish with cooking spray.
Heat a skillet over medium high heat, and cook the beef with onion, bell pepper, and garlic. Crumble the beef as you cook it, and cook until cooked through (6-7 minutes). Drain fat.
Add diced tomatoes, ketchup, brown sugar, mustard, Worcestershire sauce, and corn. Cook together for 4-5 minutes. Season with salt and pepper, taste the sauce and adjust seasonings to your preference.
Transfer the sloppy joe mixture to the prepared 9x13 baking dish, then sprinkle with half of the cheddar and colby cheese. Arrange the frozen tater tots in a single layer on top.
Bake for 30-40 minutes or until the tater tots are crispy. Sprinkle the remaining colby and cheddar cheese on top, and place under the broiler for a few minutes, or until the cheese is melted. Allow to cool for 15 minutes before serving, garnished with chopped parsley.