Preheat your oven to 375°F. Spray a 9×13 inch baking dish with cooking spray and set aside.

In a large skillet over medium high heat, cook ground beef and diced onion together, breaking up the meat as it cooks. Season with salt, black pepper, and garlic powder. Cook for 8 to 10 minutes until beef is completely browned and onions are softened.

Use a colander to drain ALL the grease from the cooked beef mixture. This step is crucial for preventing a greasy casserole. Return the drained beef to the skillet and set aside.

In a large mixing bowl, combine cream of mushroom soup, sour cream, drained corn, and undrained Rotel tomatoes. Stir in 1 cup of shredded cheddar cheese. Mix everything together until well combined and creamy.

Spread the cooked ground beef mixture evenly across the bottom of the prepared baking dish. Pour the creamy soup mixture over the beef layer and spread it out gently to cover all the meat completely.

Arrange frozen tater tots in a single layer over the creamy mixture, packing them close together. The tater tots should cover the entire surface for maximum crispy coverage.

Place the baking dish in the preheated oven and bake uncovered for 35 to 40 minutes, until the tater tots are golden brown and crispy and the casserole is bubbling around the edges.

Remove the casserole from the oven and immediately sprinkle the remaining 1 cup of shredded cheddar cheese evenly over the hot tater tots. Return to the oven for 5 more minutes until the cheese is completely melted.

Let the casserole rest for 5 minutes before serving. This allows the layers to set up properly and makes serving much easier.

Cut into portions and serve hot. Garnish with sliced green onions, extra sour cream, or bacon bits if desired. Enjoy your hearty Cowboy Casserole!