In a large pot, over medium heat, place the olive oil, onions, scallions and garlic. Cook for 5 minutes.
Add the fish stock, achiote, ground cumin and bring to a boil. Then reduce the heat to medium-low. Add the plantains, corn, yuca, salt and pepper. Simmer covered for about 25 to 30 minutes.
Add the fish and chopped cilantro. Cook for 12 minutes and serve with white rice, lime and avocado on the side.