For the chicken, using a mortar and pestle, pound the lemongrass with the salt and sugar to make a rough paste. Add the garlic and coriander root or stems and continue to pound to a paste. Add the crushed black peppercorns and pound until you have a semi-smooth paste. Finally, add the fish sauce and mix until well blended.
Rub the chicken pieces thoroughly with the paste, and marinate, covered, in the refrigerator for at least two hours.
Preheat a ridged cast-iron grill pan until hot, but not too hot. Alternatively, light a barbecue outdoors and wait until the flames have died down and the coals are turning white.
Place the chicken in the pan or on the barbecue where it is not too close to the direct heat. Cook the chicken in the grill pan or over the barbecue slowly in order to impart a smoky savoury character and allow the marinade to caramelise.
Turn the chicken pieces frequently (every three minutes or so) to prevent them from burning. Cook for 10-15 minutes, or until cooked through and caramelised (the chicken is cooked when the juices run clear when the chicken is pierced in the thickest part with a skewer).
For the dressing, dry-roast the nuts in a heavy-based pan (without oil) over a medium heat until golden-brown. Shake the pan occasionally, being careful not to scorch the nuts. Remove from the heat and allow the nuts to cool.
Using a mortar and pestle, grind the ginger, chillies and shallots to a paste. Add the roasted nuts and continue to crush, then add the palm sugar and work until smooth. Add the remaining dressing ingredients and mix together. The dressing will be sweet, hot, salty and sour.
For the bean curd salad, half-fill a deep, heavy-based pan with the vegetable oil and heat until a cube of bread dropped in sizzles and turns golden-brown in 30 seconds. (CAUTION: Hot oil can be dangerous. Do not leave unattended.)
Pat the bean curd dry with kitchen paper, then deep-fry in the hot oil for 4-5 minutes, or until golden-brown all over. Remove with a slotted spoon, drain on kitchen paper and cut into ½cm/¼in slices.
Bring a pan of salted water to the boil. Cook the mangetout and bean sprouts in the boiling water for 30 seconds, then quickly refresh under cold running water to stop them from cooking further. Mix the blanched vegetables with the cucumber and red pepper. Scatter over the fried slices of bean curd, the spring onions and coriander leaves.
To serve, spoon the roasted nut and tamarind dressing over the top of the salad and pile the chicken alongside. The salad is best eaten straightaway.