Heat the olive oil in a large, heavy soup pot or Dutch oven over low heat. Add the onion and all the bell peppers and sweat about 5 minutes, or until nicely softened. Stir in the tomatoes, salt, pepper, and chiles and cook about 2 minutes more. Pour in the fish stock and coconut milk and bring to a boil over medium-high heat. Reduce to a simmer and cook 10 to 15 minutes, stirring occasionally, until the peppers are tender.