1. Preheat the oven to 375°F and grease a 9×13-inch baking dish.

2. Cook the ground beef and chopped onion in a large skillet over medium heat until the beef is browned and the onion is soft. Drain excess grease.

3. Stir in the minced garlic, salt, and black pepper, and cook for 30 seconds.

4. Add the cream of mushroom soup, sour cream, and 1 cup of shredded cheddar cheese. Stir until the mixture is creamy and combined.

5. Spread the beef mixture evenly into the prepared baking dish.

6. Arrange the frozen tater tots in a single layer over the top.

7. Bake for 30 minutes, or until the tater tots are hot and starting to turn golden.

8. Sprinkle the remaining 1 cup of cheddar cheese over the top.

9. Return the casserole to the oven and bake for 10 more minutes, until the cheese is melted and bubbly.

10. Remove from the oven, top with sliced green onions, let rest for 5 minutes, and serve.