Dice the onion, bell pepper, and tomato. Heat 2 tablespoons of olive oil over medium-low heat in a large pot and add diced vegetables. Cook until tender, about 10 minutes. Meanwhile, peel and slice green plantains and sweet potato.
Mince garlic and herbs and add to pot. Cook for 5 minutes, stirring occasionally. Continue prepping plantains and potato, if necessary.
Add sliced plantains and sweet potato, and shrimp to pot along with coconut milk and chicken stock. Turn heat up to medium and cook for 45 minutes or until all seafood is fully cooked and plantains/sweet potato are tender.
Meanwhile, heat the remaining 2 tablespoons of olive oil in a pan. Season fish fillet with salt and pepper and fry it in the pan until done. Then set aside.
Chop fish and add to stew right before serving or in the bowl.