01 - Preheat oven to 375°F. Lightly grease a 9x13-inch baking dish with cooking spray or butter.
02 - Heat a large skillet over medium heat. Add ground beef and chopped onion. Cook, breaking up the beef with a spoon, until 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 and heated through.
04 - Spread the beef mixture evenly in the prepared baking dish. Sprinkle 1 cup cheddar cheese over the top. Arrange tater tots in a single layer over the cheese.
05 - Bake uncovered for 35–40 minutes, until tater tots are golden brown and crispy.
06 - Remove from oven and sprinkle remaining cheddar cheese over the casserole. Return to oven for 5 minutes, until cheese is melted and bubbly.
07 - Let the casserole rest for 5 minutes before serving to allow the filling to set.