Bring a large pan of water to a rolling boil and drop in the spinach. As soon as it wilts drain it and leave in the colander.
Heat oil in a wok over a medium high heat. When hot add the garlic and stir and fry until light brown. Add the chillies and stir once or twice.
Add the spinach to the pan with the stock, fish sauce and salt. Turn the heat to high and fry for 1-2 minutes until the spinach is well flavoured with the other ingredients.