1.Combine pork and char siu. Cover and place in fridge to marinate for 1 hour.
2.Heat 1tbsp rice bran oil in a wok or large frying pan on medium. Add apples and onions, cook 5 minutes, stirring, until onion has softened and apples are starting to brown. Remove from wok.
3.Heat remaining oil in wok. Stir-fry pork in batches 3-5 minutes, until cooked through. Return apples and onions to wok with water chestnuts and spinach. Stir-fry 2-3 minutes, until chestnuts are heated through and spinach has wilted.
4.Sprinkle with sesame seeds and serve with steamed rice.