If using bamboo skewers, soak in cold water for at least 30 minutes.
Cut the prawns in half lengthways down to the tail, and flatten out to form a symmetrical shape.
Thread a prawn onto two skewers, with the tail in the middle. Thread another 3 prawns onto the same two skewers in the same way. Repeat until you have four sets of 4 prawns on each two skewers.
Lay the skewered prawns in a glass or ceramic dish. Sprinkle the lime juice over them. Combine the spices and oil in a small bowl, and use to coat the prawns well. Cover and chill for 2 hours.
Cook the prawns on a foil-lined grill pan under a hot grill for 6 minutes, turning halfway through cooking. Serve immediately.