Preheat oven to 375°F (190°C). Grease a 9x13-inch baking dish.
In a skillet over medium heat, cook ground beef and diced onion until fully browned. Drain excess grease.
Stir in cream of mushroom soup, sour cream, 1 cup of cheese, salt, and pepper. Mix until smooth.
Spread the beef mixture into the bottom of the prepared baking dish.
Arrange tater tots in an even layer over the top.
Sprinkle with remaining cheese.
Bake for 35-40 minutes until bubbly and tots are crispy and golden.
Serve hot with a side of vegetables or salad.