01 - Preheat oven to 375°F. Lightly grease a 9x13-inch baking dish with cooking spray or butter.
02 - In a large skillet over medium heat, cook ground beef and chopped onion until beef is browned and onion is soft, about 6–8 minutes. Drain excess fat.
03 - Stir in mixed vegetables, cream of mushroom soup, milk, ketchup, Worcestershire sauce, garlic powder, onion powder, salt, and black pepper. Simmer for 2–3 minutes until well combined.
04 - Spread the beef mixture evenly in the prepared baking dish. Sprinkle 1 cup cheddar cheese over the mixture.
05 - Arrange frozen tater tots in a single layer over the top, covering the entire surface.
06 - Bake uncovered for 35–40 minutes, until tater tots are golden and crispy.
07 - Remove from oven and sprinkle remaining cheddar cheese over the casserole. Return to oven for 5 minutes, until cheese is melted and bubbly.
08 - Let the casserole rest for 5 minutes before serving to allow the layers to set.