Heat a pan until almost smoking. Put the prawn skewers and lemongrass on for 2-3 mins, turning once – don’t overcook.
Mix the marinade ingredients and add to the prawns. Leave for 5 mins. To cook on a barbecue: thread the prawns on metal skewers, place in the centre of the grill on the lemongrass and cook for 2-3 mins, turning once until opaque. Discard the lemongrass before eating.