Put the noodles in a bowl and pour over boiling water to cover them. Set aside to soak for 10 mins. Stir together the orange juice and zest, curry paste, fish sauce, sugar and 3 tbsp water to make a sauce.
Heat the oil in a large wok and add half the ginger and the garlic. Cook, stirring, for 1 min. Add the pepper and stir-fry for 3 mins more. Toss in the sugar snaps, cook briefly, then pour in the curry sauce. Add the beansprouts and prawns, and continue cooking until the prawns just turn pink. Drain the noodles, then toss these into the pan with the herbs and remaining ginger. Mix until the noodles are well coated in the sauce, then serve.