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 for 6 to 8 minutes, breaking up the beef with a spoon, until beef is browned and onion is softened. Drain excess fat from the skillet.
03 - Stir in mixed vegetables, cream of mushroom soup, milk, ketchup, Worcestershire sauce, garlic powder, onion powder, salt, and black pepper. Simmer for 2 to 3 minutes, stirring constantly, until everything is well combined and heated through.
04 - Spread the beef mixture evenly in the prepared baking dish. Sprinkle 1 cup of shredded cheddar cheese over the top of the mixture.
05 - Arrange frozen tater tots in a single, even layer over the cheese-topped beef mixture.
06 - Bake uncovered for 35 to 40 minutes, until tater tots are golden brown and crispy.
07 - Remove the casserole from the oven. Sprinkle the remaining 1 cup of shredded cheddar cheese evenly over the top. Return to the oven for 5 minutes, or until cheese is melted and bubbly.
08 - Let the casserole rest for 5 minutes before serving to allow the filling to set.