Bathe fish, clean and divide into fillet. Cook the stock of bones and heads, adding onion and carrot. Filter.

Cut the remaining onion into half-rings, sautee in a part of butter. Sautee tomato puree apart. Peel pickled cucumbers, remove seeds, cut into slices and simmer.

Put sliced potatoes in boiling fish stock, add fish slices and cook for 10 minutes over law heat, then add sautéed onion, tomato puree, cucumbers, spices and cook for additional 5 minutes. If desired, put cooked and sliced mushrooms. Cook for 5 minutes.

When serving, add chopped greens, olives, and (if there is no mushrooms) one lemon slice.