Place prawns in a bowl with lemon juice and a pinch of salt. Mix well and put aside for 15 minutes then wash them and pat dry.
Mix all the marinade ingredients together and add it to the prawns. Cover and put in the fridge for at lest one hour.
Beat the batter ingredients together. Heat the sunflower oil in a small pan. Coat each prawn in cornflour, shaking off the excess, then dip into batter and drop into hot oil. Deep fry until golden for 2-3 minutes. Don't overload the pan; you should be able to cook 3 or 4 at once.
Drain on kitchen paper and serve with a sweet chilli dipping sauce.