Preheat oven to 375°F (190°C).
In a large skillet over medium heat, cook ground beef until browned, breaking it apart with a spoon, about 5-7 minutes.
Add diced onion and minced garlic to the skillet. Cook until onion is translucent, about 3-4 minutes. Drain excess fat.
In a large mixing bowl, combine the cooked ground beef mixture, cream of mushroom soup, sour cream, frozen mixed vegetables, salt, and black pepper. Stir until well combined.
Transfer the mixture to a 9×13 inch baking dish and spread evenly.
Sprinkle shredded cheddar cheese evenly over the beef mixture.
Arrange frozen tater tots in a single layer on top of the cheese.
Cover the baking dish tightly with aluminum foil and bake for 35 minutes.
Remove the foil and bake for an additional 10 minutes, or until the tater tots are golden brown and crispy.
Remove from oven and let cool slightly before serving.