Rinse the prawns. Using kitchen scissors, trim the legs and feelers off the prawns. Cut through the shell along the back of each prawn and remove the digestive tract.
Heat the wok, add 2 tbsp oil and stir-fry prawn with ginger for 30 seconds. Transfer to a plate.
Reheat the wok, combine the sugar with 2tbsp water over medium heat. Cook and stirring the mixture for 5minitues or until the mixture has thickened and smells caramelized.
Add water, soy sauce, and oyster sauce, swirling the pan to combine everything. Add the prawns. Cover the wok and bring the caramel mixture to a simmer and cook for 5 minutes or until the sauce reduce to a stick coating.
Add sault if need, serve garnished with spring onion.