Preheat oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish.
In a large skillet over medium heat, cook ground beef and diced onion until beef is browned and no longer pink, about 8–10 minutes. Drain excess fat.
Add minced garlic and cook for 1 minute more. Stir in cream of mushroom soup, milk, thawed mixed vegetables, 1 cup of shredded cheddar cheese, salt, pepper, and Worcestershire sauce (if using). Mix well and pour into the prepared baking dish.
Top the mixture evenly with frozen tater tots, pressing them down slightly to adhere.
Bake uncovered for 40–45 minutes, or until the tater tots are golden brown and crispy and the casserole is heated through.
Remove from oven and sprinkle remaining 1 cup of shredded cheddar cheese on top. Let stand for 5 minutes before serving.
Notes
Serve hot as a hearty main dish. Great with a side salad or steamed green beans.