In a large bowl, combine ground meat, rice, half the diced onion, half the cilantro, egg, and minced garlic. Season with salt, pepper, and cumin. Mix gently until just combined. Form into 1-inch meatballs.

Pour beef or chicken broth into a large pot and bring to a gentle boil over medium-high heat. Carefully drop meatballs into the boiling broth one at a time, stirring occasionally.

Once all meatballs are in the pot and begin to float (about 10 minutes), add the diced potatoes, carrots, and zucchini. Stir well and reduce heat to medium.

Pour in the canned diced tomatoes with their juice. Stir the remaining minced garlic into the broth. Season with additional salt, pepper, and cumin to taste.

Allow the soup to simmer gently for 20-25 minutes until the vegetables are tender and the meatballs are cooked through.

Taste and adjust seasonings as needed. Stir in the remaining fresh cilantro just before serving.

Ladle into bowls and serve hot with lime wedges, warm tortillas, and additional cilantro on the side.