Cut the pork, shrimp, ham, chicken, mushroom, if using, into small dice. Thinly slice the spring onion greens. Beat the egg with a little salt and pepper. Break the rice up into small clumps to make it easier to fry.
Heat 2 tablespoons of the oil in a wok over a high flame. Add the pork and stir-fry briefly until the pork is pale. Add the ham, chicken, shrimp, mushrooms, peas, and continue to stir-fry for 1–2 minutes, until everything is hot and sizzling. Add the Chinese rice wine, then pour in the stock and bring to the boil. Season with salt, then pour off into a bowl and set aside.
Rinse and dry the wok and return it to the heat with the remaining oil. When the oil is hot, add the beaten egg mixture and swirl it around the base of the wok. When the egg is half-cooked, add the green onions and all the rice and stir-fry, breaking up any clumps.
When the rice is very hot, smells delicious and makes a popping sound around the edges of the wok, add the reserved ingredients in their stock sauce. Mix well and continue to stir-fry for another 30 seconds or so, seasoning with salt or pepper if you wish.