In a large skillet, cook the ground beef and chopped onion over medium heat until the beef is browned and the onion is tender. Drain any excess fat.
In a mixing bowl, combine the cooked beef mixture, cream of mushroom soup, and 1 cup of shredded cheddar cheese. Mix well.
Spread the beef mixture evenly in a baking dish. Top with an even layer of frozen tater tots.
Bake in the preheated oven for 30 minutes. Remove from the oven and sprinkle the remaining 1 cup of shredded cheddar cheese on top. Return to the oven and bake for an additional 15 minutes, or until the cheese is melted and bubbly.
Let the casserole cool for a few minutes before serving. Enjoy!
Notes:
This casserole is a great make-ahead meal. You can prepare it up to the baking step and refrigerate it until you're ready to bake.