1) Preheat griddle or griddle pan over high heat.
2) Butterfly shrimp by slicing almost through lengthwise, but leave shell on prawns, this will keep the prawns tender while cooking over such high heat.
3) Brush prawns with oil, season with salt and pepper and griddle 2 minutes on each side, until shells are hot pink and prawns are opaque. Place lemons on griddle during the last minute. The heat will release the juice from the lemons.
4) To serve, squeeze grilled lemon wedges over prawns.