Cook the rice at least 2 hours ahead of time or the night before. Allow it to cool thoroughly and put in the refrigerator.
Heat a wok or large frying pan over high heat until it is hot. Add the oil, and when it is very hot and slightly smoking, add the garlic and onion and stir-fry for 2 minutes. Add the mushrooms and cook for 2 minutes more. Then add the rice and stir-fry for 3 minutes. Add the turmeric, pepper, sugar and curry powder and continue to stir-fry for 2 minutes, then add the fish sauce and stir-fry for 1 more minute.
Turn onto a platter, garnish with the spring onions and serve hot, or cold as a rice salad.