Bring a large saucepan of salted water to the boil. In a large bowl, whisk together all the dressing ingredients. Put the cucumber halves cut-side down on a chopping board and bash with a rolling pin so they crack in places. Roughly chop and tip into the dressing; toss together. Set aside until ready to serve.
Add the noodles to the pan of boiling water, then take off the heat and leave to stand for 5 minutes. Drain in a sieve, rinse briefly under cold water; shake dry. Tip into the bowl with the cucumber and dressing. Add the salad onions and toss everything together
Divide the noodles and cucumber between 2 plates or shallow bowls and top with the flaked salmon. Scatter with chilli sea salt and serve.
