Peel the cucumbers, slice in half lengthways and, using a teaspoon, remove the seeds. Then cut into 2.5cm (1 in) cubes. Sprinkle them with the salt and combine thoroughly. Put into a colander and leave to stand for 20 Minutes to drain. This gets rid of any excess liquid.
While they are draining, prepare the prawns. If using frozen prawns, defrost thoroughly. Peel, and discard the shells. Using a small, sharp knife, remove the fine digestive cord. Wash them, drain and pat dry with kitchen paper. In a large bowl, combine the marinade ingredients. Add the prawns, mix well and marinate for 15 Minutes in the refrigerator. Drain, discarding the marinade.
When the cucumber has drained for 20 Minutes, rinse thoroughly in cold water and blot dry with kitchen paper.
Heat a wok over high heat until it is hot and then add the oil. When the oil is very hot and slightly smoking, add the garlic, ginger and cucumber and stir-fry for 3 Minutes.
Add the prawns, salt and pepper, and stir-fry for 4 Minutes or until the prawns turn pink.
Then stir in the sesame oil, give the mixture a couple of good stirs and leave to cook undisturbed for another 3 Minutes.