Preheat your oven to 350°F. Grease a 9x13-inch baking dish.
In a large skillet, cook the ground beef and diced onion over medium heat until the beef is browned and the onion is softened. Drain any excess fat.
1 pound ground beef, 1 small onion
In a large bowl, combine the cooked ground beef and onion mixture, cream of mushroom soup, sour cream, thawed hashbrowns, cheddar cheese, salt, garlic powder, onion powder, and pepper. Mix until well combined.
10 ½ ounce can cream of mushroom soup, 1 cup sour cream, 26 to 30 ounce package frozen hashbrowns, 1 ½ teaspoons salt, 1 teaspoon garlic powder, 1 teaspoon onion powder, ½ teaspoon ground black pepper, 1 cup shredded cheddar cheese
Spread the mixture evenly into the prepared baking dish. Sprinkle the cheese over the top of the casserole, then add the french fried onions.
6 ounces french fried onions, 1 cup shredded cheddar cheese
Cover, and bake for 45-50 minutes, or until the casserole is bubbly. Uncover and bake for an additional 5 minutes or until the french fried onions are golden brown.
Let the casserole cool for a few minutes before serving.