Heat oil in a pan or wok and stir fry garlic, ginger and spring
onion for about 20 seconds. Add prawns, mushrooms and water chestnuts and stir fry for about
2 minutes. Add fish sauce and sugar, stir for a few times, then add stock
or water. Bring to the boil and stir for another minute or so. Finally, add chili sauce, if using, and season with salt and
pepper. Garnish with coriander sprigs and serve at once.