Preheat oven to 375°F (190°C). Grease a 9×13-inch baking dish.
- In a skillet, cook ground beef and onion over medium heat until browned. Drain excess fat.
- Add garlic, salt, and pepper; cook 1 minute until fragrant.
- Stir in cream of mushroom soup and milk until combined.
- Add mixed vegetables (if using) and stir to distribute.
- Spread beef mixture evenly in baking dish.
- Sprinkle shredded cheese on top.
- Arrange tater tots in a single layer over cheese.
- Bake uncovered 35–40 minutes, until bubbly and tater tots are golden.
- Rest 5 minutes before serving.