Preheat the oven to 350°F (175°C).
In a skillet, brown the ground beef over medium heat, breaking it apart as it cooks.
Add the diced onion and cook until translucent, about 5 minutes.
Stir in the frozen mixed vegetables and garlic powder, cooking for an additional 3 minutes.
Add the cream of mushroom soup, mixing until evenly combined.
Season with black pepper, stirring well to incorporate all flavors.
Spread the filling evenly in a greased 9x13-inch baking dish.
Top with the frozen tater tots in a single layer.
Sprinkle the shredded cheddar cheese over the tater tots, covering them completely.
Bake in the preheated oven for 45-50 minutes, or until the tater tots are golden brown.
Let the casserole cool for 5-10 minutes before serving.