Mix together the sauce ingredients and set aside. Peel the prawns and discard the shells. Combine them with salt, cornstarch, and 1 tsp toasted sesame oil. Heat a wok or large skillet, then add the peanut oil, prawns, and ginger. Stir-fry the mixture for 30 seconds. Then add the sauce ingredients and continue to cook for 2 minutes. Serve at once.