Place the prawns and lime zest in a large, non-metallic bowl. Place the lime juice, chillies, garlic, ginger and onion in a food processor or blender, and process until smooth. You may need to add a little oil to facilitate blending. Pour over the bowl of prawns, and stir to coat. Cover, and refrigerate for 4 hours.
Preheat barbecue for medium-high heat. Thread prawns onto skewers, piercing each first through the tail, and then the head.
Brush cooking grate with oil. Cook prawns for 5 minutes, turning once, or until opaque.