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 beef with a spoon, until beef is browned and onion is softened, approximately 6–8 minutes. 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 the mixture for 2–3 minutes, stirring constantly, until all ingredients are well combined and heated through.
04 - Transfer the beef mixture to the prepared baking dish, spreading it evenly across the bottom. Sprinkle 1 cup of shredded cheddar cheese over the meat mixture.
05 - Arrange frozen tater tots in a single, even layer over the cheese and beef mixture. Place them close together for maximum coverage.
06 - Bake uncovered for 35–40 minutes, or until tater tots are golden brown and crispy. The filling should be bubbly around the edges.
07 - Remove the casserole from the oven. Sprinkle the remaining 1 cup of cheddar cheese evenly over the top. Return to the oven and bake for an additional 5 minutes, or until cheese is fully melted and slightly bubbly.
08 - Let the casserole rest for 5 minutes before serving to allow the filling to set slightly. Serve warm.