Preheat the oven to 375°F (190°C).
In a large skillet over medium-high heat, cook the ground beef, diced onion, and minced garlic until the beef is browned and the onion is translucent, about 7-8 minutes. Drain any excess grease.
Add the frozen mixed vegetables to the skillet and cook for 3-4 minutes, stirring occasionally, until the vegetables are slightly softened.
In a medium bowl, combine the condensed cream of mushroom soup, sour cream, milk, Worcestershire sauce, salt, and black pepper. Stir until smooth.
Pour the soup mixture into the skillet with the beef and vegetables. Stir well to combine and heat through for 2-3 minutes.
Transfer the beef and vegetable mixture to 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 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.