Wash the fish, dab dry and cut into 8 equal slices, season with salt and pepper. Wrap fish fillets in ham. Heat 2 tablespoons of oil in a large frying pan. Fry the fish fillets for 5-6 minutes while turning.
Cucumbers wash, so peel, that always a piece of peel remains, remove the core, cut cucumber into sticks. Onions peel and chop finely. Heat 1 tablespoon of oil in a wide saucepan. Sauté onions, add cucumber and steam for about 2 minutes, dust with sugar and let caramelize.
Deglaze with vinegar and cream and simmer for 2-3 minutes, season with coarse mustard, salt and pepper. Stir starch and 2 tablespoons of water until smooth, thicken vegetables with it.
Arrange fish and vegetables on plates, add remaining vegetables. Sprinkle with coarse pepper.