Use a cheese slicer to cut the cucumber lengthways into slices. Use the first slices for other purposes. Cover the cucumber slices with salmon slices. Refine with horseradish cream, roll up and stand upright. Decorate with the roe as a substitute for caviar.
Note: I stole this idea from Ulrika Jisland and Anna Jonasson in Sweden. But I have permission from the nice ladies to publish this ingenious recipe.