Preheat the oven to 375°F (190°C).
Brown the meat: In a large skillet, cook the ground beef over medium heat until browned, about 5-7 minutes. Use a wooden spoon to break up the meat as it cooks. Drain any excess fat.
Sauté the onion: Add the chopped onion to the skillet with the browned meat and cook until softened, about 2-3 minutes.
Mix the casserole base: In a mixing bowl, combine the cream of mushroom soup, sour cream, 1 1/2 cups of shredded cheddar cheese, garlic powder, onion powder, salt, and pepper. Stir to combine, then add the beef and onion mixture. Mix well.
Assemble the casserole: Transfer the meat and soup mixture into a greased 9x13-inch baking dish. Spread it out evenly.
Top with tater tots: Arrange the frozen tater tots in a single layer over the casserole mixture, covering it completely.
Bake: Cover the casserole with aluminum foil and bake for 30 minutes. After 30 minutes, remove the foil and bake for an additional 15 minutes, or until the tater tots are golden and crispy.
Add cheese: Sprinkle the remaining 1/2 cup of shredded cheddar cheese on top of the casserole, then return it to the oven for 5 more minutes until the cheese is melted and bubbly.
Serve and enjoy: Let the casserole cool for a few minutes before serving. Enjoy this comforting, cheesy goodness!