Either with a mandolin or using a vegetable knife, thinly slice the cucumber lengthways. Place in a sieve and sprinkle with sea salt to draw some of the liquid out of the cucumber. Pat dry after 5 minutes.
Steam the Tenderstem broccoli for 3-4 minutes.
Mix all the dressing ingredients together and season with salt and pepper.
Combine with the cucumber and Tenderstem broccoli with the red onion, spring onions and coriander. Toss with the dressing and serve.