Start by making the dressing. Pound the chillies, garlic and salt to form a rough paste using a pestle and mortar. Transfer to a bowl and stir in the coriander, palm sugar, fish sauce and lime juice, then stir until the sugar has dissolved.
Loosen the scallops from their shells with a small knife. Place the shells on a hot barbecue and cook for 3 minutes. Arrange the shells on plates and top each one with a spoonful of the dressing. Serve hot.
Alternatively, thread shelled scallops on to bamboo skewers that have been soaked in cold water for 30 minutes. Cook for 1 minute on each side and serve with the dressing.