Preheat the oven to 350°F (175°C).
In a skillet, brown the ground beef and chopped onion over medium heat until the beef is no longer pink. Drain excess fat.
Stir in the rice, cream of mushroom soup, beef broth, garlic powder, onion powder, and optional mixed vegetables. Season with salt and pepper to taste.
Pour the mixture into a greased 9x13 inch baking dish.
Cover with aluminum foil and bake in the preheated oven for 30 minutes.
Remove the foil, stir the casserole, and sprinkle the shredded cheddar cheese on top.
Return to the oven and bake uncovered for an additional 10-15 minutes, or until the cheese is melted and bubbly.
Let it cool for a few minutes before serving.