For the stock (optional), bring all ingredients to a boil in a large stock pot. Once boiling, bring to a simmer on low heat and simmer for at least 4 hours. Strain and reserve the stock, discarding the chicken, vegetables, and herbs.
To prepare the meatballs, combine the ground beef, chorizo, egg, milk, breadcrumbs, cilantro, and salt and pepper in a bowl. Either mix with a spoon or with your hands. Once combined, roll into golf ball-sized balls and set aside.
Drizzle about 2 tablespoons of olive oil in a large stock pot over medium heat. Add the onion, garlic, and jalapeno and cook until the onions are translucent, about 4 minutes.
Add the cumin and a bit of salt and pepper. Add both cans of tomatoes (with juices) and bring to a boil. Bring back down to a simmer.
Add the corn kernels, rice, and meatballs. Simmer for at least 25 minutes, or until the rice is tender and the meatballs have cooked through. Serve topped with cheese, avocado, cilantro, or fresh lime wedges.