Wash cucumbers thoroughly and dab dry, clean. Halve the cucumbers lengthwise and remove the seeds with a tablespoon. Cut the cucumber halves into 3 diagonal pieces. Cut cucumber remains into fine cubes
Peel and chop the onion. Mix with quark, yoghurt and horseradish. Season to taste with salt and pepper. Fold in cucumber cubes. Pour the horseradish cream into the boats and arrange on a plate
Cut the salmon into slices with a sharp knife and distribute them on the boats. Garnish with lettuce, lemon and dill