Heat a wok over high heat. Add enough sesame oil to lightly coat the bottom of the wok. Add the garlic and ginger and stir-fry for 30 seconds. Add the sausage and stir-fry for another 1 minute. Add the spinach and bok choy and cook quickly until just slightly wilted, about 30 seconds. Add the rice and soy sauce and toss until the ingredients are combined well and the rice is heated through.