Marinating the Chicken
In a mini food processor, process the coriander, fish sauce and pepper to a coarse puree. Coat the chicken with the marinade.
Let stand at room temperature for 20 minutes.
Preheat the oven gas mark 7 or 180.
Griddle
Rub the chicken with oil and rub the griddle with an oiled paper towel. Griddle the chicken over a moderately high heat, turning, until charred, approximately 12 minutes. Transfer the chicken to a baking sheet and roast for 30 minutes, until cooked.
Preparing the Dipping sauce
In a bowl, combine the dissolved tamarind with the fish sauce, lime, garlic, chilli, sugar and water.
Just before serving, stir the coriander into the dipping sauce and serve with the chicken.