Peel the cucumbers, cut in half and remove the seeds with a spoon. Cut the cucumber halves crosswise into strips.
Peel and dice the onions and sauté in oil. Add the cucumbers, sauté briefly, dust with flour
and sauté. Pour in the soup and crème fraîche. Stir in the mustard and chopped dill and season with salt and pepper. Simmer until the gherkins are nearly al dente. Cut the fish fillet into wide strips and season with salt, pepper and lemon juice. Place the fish on top of the ragout, cover and simmer for approx. 5 minutes.