In a heavy-based frying pan, bring to the boil the palm sugar, fish sauce and coconut milk. Once it's boiling, drop in the chicken thighs and make sure all pieces are covered by the liquid. Simmer for a good 10 minutes, turning once or twice. Once cooked, leave to cool in the liquid.
Peel and slice the shallots very finely, remove the seeds from the pepper and the chillies and cut into long thin strips.
Cut the cucumber down the centre lengthwise and remove the seeds. Using a potato peeler, peel long strips of the cucumber until all used up.
Chop the roasted peanuts and mix them with the coriander. Mix the pepper, shallots, chillies and cucumber in a bowl and leave to sit.
When cool, take the chicken from the liquid and, using a sharp knife, remove any skin and discard. Cut the chicken into thin strips about the same size as the pepper and chillies. Add the chicken to the vegetable mix, then add the coconut milk mixture.
Toss well together and place in a large bowl. Sprinkle with the chopped nuts and the coriander to serve.