In a small stock pot, heat the vegetable oil. When the oil is hot, add the Andouille and render for 3 to 4 minutes. Stir in the onions and celery. Cook the vegetables for 2 to 3 minutes, or until the vegetables start to wilt. Season the vegetables with salt and cayenne. Stir in the garlic, beans, and bay leaves. Add the water and bring the liquid up to a boil. Reduce to a simmer and cook for 3 hours, uncovered, or until the beans are soft and creamy. Stir the mixture occasionally and check the seasonings for salt and cayenne. Stir in the green onions. Serve the beans with the pan-fried fish.