Place the rice in a heatproof bowl. Bring the water to a boil and pour it over the rice. Let soak for 40 minutes, then drain; set aside. Meanwhile, in a saute pan over medium heat, warm 2 tablespoons of the vegetable oil. Add 1 of the onions and saute until soft, about 5 minutes. Remove from the heat and let cool. In a bowl, combine the pork, beef, cooled onion, soaked rice, egg, cumin, oregano, 3/4 teaspoon of the salt and 1/2 teaspoon of the pepper. Using your hands, mix well and form into 1-inch balls. In a large soup pot over medium heat, warm the remaining 2 tablespoons vegetable oil. Add the remaining onion and saute until soft, about 5 minutes. Add the garlic, zucchini, carrots and tomatoes and cook, stirring, until fragrant, about 5 minutes. Add the chicken stock, stir well and bring to a boil. Carefully slip the meatballs into the pot, reduce the heat to low and simmer uncovered until the meatballs are fully cooked, about 45 minutes. Stir in the remaining 3/4 teaspoon salt and 1/2 teaspoon pepper. While the soup simmers, make the cilantro pesto: In a mini food processor or a blender, combine the cilantro, mint, lime juice, olive oil, water and salt. Process to a paste. Ladle the soup into warmed soup bowls and top each serving with a dollop of cilantro pesto. Serve at once.
