In a mixing bowl, combine ground beef, cooked rice, beaten egg, garlic powder, salt, and black pepper. Mix well and form into small meatballs.
In a large pot, heat a bit of oil over medium heat. Add chopped onion and minced garlic, and sauté until softened.
Add sliced carrot and zucchini to the pot, and cook for a few minutes.
Pour in beef broth and tomato sauce. Stir in dried oregano, ground cumin, salt, and black pepper. Bring to a boil.
Gently add the meatballs to the pot. Reduce heat to a simmer and cook for about 30 minutes, until meatballs are cooked through and vegetables are tender.
Serve hot, garnished with fresh cilantro if desired.