Preheat your oven to 375°F (190°C).
In a large bowl, combine ground beef, rice, chopped onion, milk, egg, garlic powder, salt, and pepper.
Mix until well combined, but do not overmix.
Shape the mixture into meatballs, about 1.5 inches in diameter.
Place the meatballs on a baking sheet lined with parchment paper.
In a separate saucepan, heat tomato sauce over medium heat.
Add Italian seasoning to the sauce, stirring well.
Once the sauce is simmering, gently add the meatballs to the sauce.
Cover the saucepan and simmer for 25 minutes.
Serve hot with rice or pasta.