Trim the rind and fat from the pork, then cut the meat into 5 cm (2 in) cubes and place them in a large mixing bowl.
Mix together all the marinade ingredients, then spoon the mixture over the cubed pork, coating it well, and set aside for 3-4 hours, or overnight, in the refrigerator. Bring to room temperature before cooking.
Heat the oven to 200°C (400°F, gas mark 6). Spread out the marinated meat evenly in an ovenproof dish and bake it in the centre of the oven for 30 minutes, or until the onions and the edges of the meat have browned.
Blend the coconut milk powder, if using, with 250 ml (9 fl oz) of hot water. Transfer the pork mixture to a saucepan, pour the coconut milk over it and add the lemongrass, and salt to taste. Slowly bring the pan to a simmer, cover it and cook for a further 10-12 minutes.
Stir in most of the chopped chilli and the coriander, reserving a little of both for garnish. Discard the lemongrass and serve.