Preheat oven to 375°F and spray a 9x13-inch baking dish with cooking spray.
Pour the uncooked rice evenly into the bottom of the prepared baking dish.
In a large bowl, combine the marinara sauce, beef broth, Italian seasoning, and garlic powder, then pour over the rice.
Arrange the frozen meatballs on top of the rice mixture in a single layer.
Cover tightly with aluminum foil and bake for 50 minutes.
Remove foil, sprinkle with mozzarella and Parmesan cheeses, and bake uncovered for 10 more minutes until cheese is melted and bubbly.