Wash and clean the cucumber, cut off 2-3 slices for decoration and roughly dice the remaining cucumber. Cut melon into slices, remove seeds, cut flesh from skin and dice coarsely.
Halve the orange and squeeze the juice. Wash the basil, shake dry, pluck the leaves from the stalks. Blend cucumber, melon, orange juice, syrup and basil, except for a little bit for decoration, in a blender.
Divide the mixture between 2-3 glasses. Decorate with cucumber and basil and pour on Prosecco.