Wash the cucumber and slice into thin slices. Peel and finely chop the onion. Dab the dill dry and chop finely. Mix vinegar, oil, horseradish and cream. Season to taste with salt, pepper and sugar.
Mix cucumber, onion, dill and the marinade. Arrange cucumber salad on plates. Cut salmon into 8 slices and place on the cucumber salad. Garnish with dill.