Combine meat, onion, cilantro, cumin, pepper, egg and salt. Mix well and roll into small balls. Saute onions in oil for 5 minutes. Add tomatoes, salt and pepper. Simmer for 5 minutes. Add meatballs and cover, simmer for 30 minutes. Add yogurt, cayenne, mint and garlic. Simmer but do not boil for 10 minutes. Add spaghetti and serve.