Chop the onion and garlic into small pieces. Heat the oil in a saucepan and sweat the onion and garlic in it, then add the finely chopped pickles.
Fill up with water and cook for approx. 5 minutes, then cut the fish up a little and add. Bring to the boil briefly and season to taste with salt, pepper, vinegar and sugar. Serve with freshly toasted bread.