Put the noodles in a large heatproof bowl and pour boiling water over to cover. Leave for 6–8 minutes until tender, then drain and rinse well under cold running water.
Whisk together the sweet chilli sauce, fish sauce and lime juice in a bowl. Shred the chicken and toss with the dressing to coat.
Add the noodles, cucumber and chilli to the chicken mixture and toss gently to combine. Scatter over the coriander leaves and serve immediately.