Serves 4. Cut the tuna into chunks, discarding the bone. If using bonito, cut it first into slices, then with a knife or fork pull off chunks of the flesh from the bone. Heat the oil in a heatproof casserole and in it saute the chopped onions, garlic and peppers, cleaned of seeds. When they are soft, add the tomatoes, paprika, salt, pepper and chili. When tomatoes are somewhat reduced add the potatoes. Stir for a few minutes, then add the wine and water. Cover the pot and cook on a high heat until the potatoes are nearly tender, about 20 minutes. Add the fish to the casserole, cover and cook another 5 minutes, or until fish flakes easily but is still juicy. Let the casserole rest, covered, for 5 to 10 minutes before serving.