Preheat your oven to 375°F (190°C).
In a large skillet over medium-high heat, cook the ground beef until browned and cooked through, approximately 7-8 minutes.
Add diced onion and minced garlic to the skillet, cooking until the onion is soft and translucent, about 5 minutes.
Stir in condensed cream of mushroom soup, milk, salt, and black pepper until well combined.
Transfer the beef mixture to a 9x13 inch baking dish, spreading it out evenly.
Arrange frozen tater tots on top of the beef mixture in a single layer.
Bake the casserole in the preheated oven for 30-35 minutes, or until the tater tots are crispy and golden brown.
Sprinkle shredded cheddar cheese over the top of the casserole and return it to the oven for an additional 5-10 minutes, or until the cheese is melted and bubbly.
Remove the casserole from the oven and let it cool for a few minutes before serving.