Place the onions, pepper, garlic and cumin in the blender with 1/4 cup of water.In a large pot, place the beef, pork, chicken, corn, onion mixture, salt and green plantain.
Add the water and bring to a boil, then cover and reduce heat to medium and cook for about 45 minutes.
Add the potatoes and yuca. Continue cooking for 30 more minutes or until the vegetables are fork tender. Stir in the cilantro.Taste and adjust the seasoning.
Serve in large soup bowls, dividing the meat and chicken and vegetables evenly.