Creating Cowboy Casserole is straightforward when you follow these detailed steps:

1. Preheat the Oven: Begin by preheating your oven to 350°F (175°C).
2. Brown the Beef: In a skillet over medium heat, cook the ground beef until browned. Make sure to break it apart as it cooks.
3. Add Vegetables: Stir in the diced onion and cook until translucent, about 4-5 minutes. Season with garlic powder, salt, and pepper.
4. Mix in Corn and Beans: Add the drained corn and green beans to the pan, stirring to combine.
5. Combine Soup and Seasoning: In a separate bowl, mix the cream of mushroom soup with the ranch seasoning. Stir this mixture into the skillet, combining thoroughly.
6. Layer the Casserole: Spread the beef and vegetable mixture evenly in a 9×13 inch casserole dish.
7. Add Tater Tots: Pour the frozen tater tots over the top of the casserole, arranging them evenly.
8. Bake: Place the casserole in the preheated oven and bake for 40 minutes or until the tater tots are golden brown.
9. Sprinkle Cheese: Remove the dish from the oven. Sprinkle the shredded cheddar cheese over the top, then return to the oven for an additional 5 minutes until the cheese is melted.
10. Cool and Serve: Allow the casserole to cool for about 5 minutes before serving to let the layers set slightly.

These simple steps ensure that your Cowboy Casserole turns out perfectly, providing a delicious and satisfying meal for family and friends.