In a large skillet over medium heat, brown the ground beef, stirring occasionally for about 5-7 minutes until fully cooked. Add diced onion and cook until softened, about 3-4 minutes. Season with garlic powder, salt, and pepper. Drain excess grease.

Lower the heat and stir in the cream of mushroom soup and frozen mixed vegetables into the meat mixture. If using sour cream, mix it in now. If too thick, add a splash of milk or broth until desired consistency is reached. Let cool for 10 minutes.

Spread the creamy meat mixture evenly in a greased 9x13-inch baking dish. Sprinkle shredded cheese over the top. Arrange frozen tater tots neatly on top of the cheese, poking holes in each for even cooking.

Preheat oven to 375°F (190°C). Bake the casserole for 30-35 minutes until tater tots are golden brown and crispy. Let it rest for 5 minutes before serving.