Preheat the oven to 375°F (190°C).
In a large skillet over medium-high heat, cook the ground beef until browned, breaking it apart with a spoon, about 5-7 minutes.
Add the diced onion and minced garlic to the skillet with the ground beef. Cook until the onion is softened, about 3-4 minutes.
Drain any excess fat from the skillet.
Stir in the frozen mixed vegetables and cook for 2-3 minutes until they begin to thaw.
In a medium bowl, combine the condensed cream of mushroom soup, sour cream, milk, Worcestershire sauce, salt, and black pepper. Mix well.
Pour the soup mixture into the skillet with the beef and vegetables. Stir to combine and heat through for 2 minutes.
Transfer the beef and vegetable mixture into a 9×13-inch baking dish, spreading it evenly.
Sprinkle the shredded cheddar cheese evenly over the beef mixture.
Arrange the frozen tater tots in a single layer on top of the cheese.
Bake uncovered in the preheated oven for 35-40 minutes, or until the tater tots are golden brown and crispy and the casserole is bubbly.
Remove from the oven and let cool for 5 minutes before serving.