Preheat your oven to 350°F (175°C).
In a skillet, cook the ground beef and onion over medium heat until the meat is browned.
Drain excess fat from the skillet.
Add the cream of mushroom soup to the beef mixture and stir until combined.
Season with salt and pepper to taste.
Spread the beef mixture evenly in a greased 9x13 inch baking dish.
Sprinkle the shredded cheddar cheese over the beef mixture.
Arrange the frozen tater tots in a single layer on top of the cheese.
Bake in the preheated oven for 30-35 minutes, or until the tater tots are golden brown.
Let the casserole cool for a few minutes before serving.