Trim off the ends of the bok choy and chop, keeping the white parts separate from the green as they will need to cook longer. Rinse and spin or pat dry. Set aside. Heat the oil in a large skillet or wok over medium-high heat. Add the bok choy stems and garlic first; stir fry for a few minutes or until the stems start to turn a pale green. When the stems are almost cooked, add the soy sauce and leaves; cook and stir until leaves are wilted, 1 to 2 minutes.