Place the vermicelli in a large bowl and pour over boiling water to cover. Leave to stand for 3 minutes, then refresh under cold water and leave to drain.
Meanwhile, remove the seeds from the cucumber using a teaspoon and thinly slice to form crescents. Place in a bowl with the chicken, carrots, bean sprouts, chopped herbs and peanuts, then added the drained noodles and toss well.
Whisk together all the dressing ingredients, then pour over the noodles and stir well. Serve garnished with extra coriander and mint leaves.