Here's the simplest, and actually one of the best, recipes of my day in the Moroccan cooking class.
Peel and grate the cucumber, then allow to drain in a colander for several minutes. Squeeze out excess liquid. Mix with the onion, mint, lemon and sugar and stir well.
Either refrigerate for several hours for a cool salad or freeze for about an hour with a spoon in it (so that you can more easily stir it) for sorbet.
Serves 4 to 6.
-- Adapted from the Riad Merdoudi cooking class