Heat a wok until very hot then add the oil. When it starts to smoke a little add the ginger, garlic, spring onions and chilli.
Stir fry for 2 minutes and when all is sizzling and golden brown add the prawns and fennel. Cook, turning occasionally, for 3-4 minutes until the shells have turned bright pink.
Add the mustard andstir and cook for another minute, then season with a little sea salt and the lemon juice.
Eat with your fingers, licking the shells before you peel them. Finsh the vegetables with a fork.