Trim the very bottom ends of bok choy. Lay bok choy flat, and slice down the middle, lengthwise. Rinse bok choy thoroughly under running water, to make sure there is no dirt in between the leaves and bulbs
In large skillet or wok, add oil and heat over medium heat. Add garlic and ginger and cook for about 3 minutes. Be careful not to burn garlic!
Add soy sauce to wok/skillet. Next, add bok choy, flat side down. Add water, cover, and steam bok choy for about 7 minutes
Mix cornstarch and a little bit of water, and mix well to form a slurry. Move bok choy to the sides of the wok/skillet, and add slurry to middle. Combine with soy sauce, and allow sauce to thicken. Move bok choy back to middle of wok/skillet, and cook for another 2-3 minutes
To finish, sprinkle with toasted sesame seeds