Break up the cold cooked rice with your hands so the grains are loose and separated. Set aside.
Heat a wok over high heat until hot. Add the oil.
Add garlic, ginger, and shallots. Stir-fry for 30 to 45 seconds until fragrant but not browned.
Add the prawns. Stir-fry for about 1 to 2 minutes until they turn pink and are almost cooked through.
Push the prawns to one side of the wok. Pour in the beaten eggs. Let them set slightly, then gently scramble until just softly set.
Add the rice. Increase heat to high and stir-fry for 2 to 3 minutes, breaking up any clumps and mixing everything evenly.
Add soy sauce, oyster sauce, sesame oil, white pepper, and mushroom powder if using. Toss well so the rice is evenly seasoned and lightly glossy.
Add scallions and chilli if using. Stir for another 30 seconds.
Taste and adjust seasoning if needed. Serve immediately.