In a large pot, bring 6 cups of water to a boil. Add the plantains and boil until they are tender, about 20 minutes.
Drain the water from the pot and mash the plantains until they are smooth.
Add the coconut milk, onion, garlic, thyme, hot peppers, salt, and pepper to the pot with the mashed plantains. Stir everything together.
Place the pot over medium heat and bring the mixture to a simmer.
Add the fish to the pot and gently stir it into the mixture.
Cover the pot with a lid and let the mixture simmer for 20-25 minutes, or until the fish is fully cooked.
Serve the stew hot, garnished with fresh herbs if desired.