Peel the cucumber, cut in half lengthways, remove the seeds and cut it into 5mm / 1/4 inch
Put the sugar and lime juice in a large bowl, and stir together until the sugar has dissolved,
then add the fish sauce.
Toss the cucumber, shallot, coriander and chilli through the dressing, then cover and
refrigerate for 15 minutes. Just before serving, cut the snowpea shoots in half and stir through