In a large bowl, combine the ground meat, rice, cilantro, onion, egg, garlic, cumin, chili powder, salt, and black pepper. Mix until well combined, then form into small meatballs, about 1 inch in diameter.
In a large pot, bring the beef broth to a boil over medium-high heat.
Carefully add the meatballs to the boiling broth. Reduce the heat to medium and let simmer for about 10 minutes.
Add the diced tomatoes, zucchini, carrot, and corn to the pot. Stir gently and continue to simmer for an additional 15-20 minutes, or until the vegetables are tender and the meatballs are cooked through.
Stir in the chopped mint just before serving. Taste and adjust seasoning if needed.
Serve hot, garnished with additional fresh mint if desired.