Wrap one half of each chilli round the middle of each prawn then thread 5 prawns on to each of 4 metal or soaked bamboo skewers.
Place the skewers in a long shallow dish and sprinkle over the oil and sea salt. Cover the dish and leave to marinate in a cool place for about 30 minutes.
Cook the prawns on the oiled grill of a preheated barbecue or under a preheated grill for 3 minutes on each side, basting with any remaining marinade. Serve the prawns hot with lemon wedges.