Heat the oil, steam the onion, garlic and parsley in it. Put the fish on top and season with salt. Cook on a very low heat.
Put the fish on a warm plate and sprinkle with the juice of one lemon.
Steam capers, anchovies and peppers in the remaining juice for a few minutes. Sprinkle with flour and douse with clear soup. Simmer on low heat for about 5 min. Season to taste with salt and freshly ground pepper. Serve the sauce over the fish.