Place the cornflour, salt, pepper and five spice in a bowl and mix together. Add the prawns and toss in the mixture to coat them evenly. Shake of any excess.
Heat the oil in a wok over a moderate heat, until starting to smoke. Add half the prawns and cook for 2-3 minutes, then turn and cook for a further minute, until they have turned pink are lightly golden.
Remove and drain on kitchen paper. Repeat with the remaining prawns. Serve immediately with the dipping sauce and a lemon wedge to squeeze over.