Make the meatball mixture

• In a bowl, combine the ground beef, rice, egg, half of the onion, garlic, cumin, oregano, salt and pepper.
• Mix until evenly combined, then roll into small meatballs.

Sear the meatballs

• Heat the olive oil in a sauté pan over medium-high heat.
• Brown the meatballs on all sides, then set aside.

Build the soup base

• In a stockpot, soften the remaining onion, carrot, celery and potato.
• Add the tomato and tomato paste and cook briefly.
• Pour in the beef broth and bring to a simmer.

Simmer the soup

• Return the meatballs to the pot and simmer gently until cooked through and the rice is tender.
• Add the zucchini in the last minutes of cooking.

Finish and serve

• Taste and adjust the seasoning.
• Serve hot with chopped cilantro and lime wedges.