Quarter the cucumber lengthways and scoop out the seeds, then cut into 1 cm pieces. Cut the cauliflower into florets, halve each one and place in a dish with the cucumber and onion. Sprinkle over the salt and leave to stand for 1 hour.
Wash the vegetables well in cold water to remove excess salt and drain well in a colander.
Meanwhile, combine the sugar, mustard, turmeric, chill