Preheat the oven to 180 °C.
Spatchcock the chicken by cutting down along the backbone, using a sharp knife or cleaver.
Spread the chicken out flat.
Pound the coriander, chillies, garlic, brown sugar, fish sauce, shrimp paste, lime juice, lemongrass and ginger in a pestle and mortar or chop in a blender.
Mix in the soya sauce and sesame oil, to make a marinade.
Rub the marinade over the chicken and place on a roasting rack in a a roasting dish.
Pour the coconut milk over the top with lime halves.
Roast in the preheated oven for 45 minutes to one hour, or until succulent and the legs fall apart fromt eh thigh.
Baste the chicken now and again with the juices.
Cut into portions and serve with rice noodles and Spicy pineapple salad
Drizzle over some of the chicken juices.