Preheat your oven to 350°F (175°C).
In a large skillet, brown the ground beef over medium heat.
Add the chopped onion and cook until soft, about 5 minutes.
Stir in the garlic powder, chili powder, salt, and pepper, mixing well.
Add the kidney beans, diced tomatoes, frozen vegetables, and uncooked rice.
Stir everything together and pour the mixture into a greased casserole dish.
Cover with foil and bake for 45 minutes.
Remove the foil and bake for an additional 15 minutes until bubbly and the rice is tender.
Let it cool for a few minutes before serving.