How to Make It
Heat the oil in a large enameled cast-iron casserole. Add the onions, green pepper, celery and garlic and cook over moderately high heat, stirring until wilted, about 5 minutes. Add the tomato sauce and season lightly with salt, black pepper and cayenne. Simmer over moderately low heat for 30 minutes, stirring occasionally.
Generously season the fish with salt, black pepper and cayenne and add to the casserole. Pour in enough water to just cover the fish, stir gently and bring to a simmer. Reduce the heat to low and simmer gently until the fish is just cooked through, about 30 minutes; swirl the stew from time to time to mix the ingredients without breaking up the pieces of fish. Five minutes before the stew is done, add the scallion greens.