Preheat the oven to 375°F (190°C).
In a large skillet, cook the ground beef and onion over medium heat until the beef is browned and the onion is translucent.
Stir in the mixed vegetables, cream of mushroom soup, garlic powder, salt, and pepper. Mix well.
Transfer the mixture into a 9x13 inch baking dish, spreading it evenly.
Sprinkle the shredded cheddar cheese evenly over the top of the beef mixture.
Top with the frozen tater tots, arranging them in an even layer.
Bake in the preheated oven for 30-35 minutes, or until the tater tots are golden brown and the filling is bubbly.
Let the casserole cool for a few minutes before serving.