Prepare the bok choy. Rinse the bok choy thoroughly, especially between the stems, to remove any dirt. Cut large heads of bok choy in half or quarters lengthwise, leaving baby bok choy whole.
Sauté aromatics. Heat the vegetable oil in a large skillet or wok over medium-high heat. Add the minced garlic and cook until fragrant, about 30 seconds to 1 minute.
Stir-fry the bok choy. Add the bok choy to the pan and toss to coat with the oil and garlic. For halved bok choy, you can place them cut-side down first for a light sear.
Cover and steam. Add the water or broth, then cover the skillet with a lid. Reduce the heat and let the bok choy steam for 2 to 3 minutes, or until the stems are tender-crisp.
Finish the dish. Uncover the pan and add the soy sauce and sesame oil. Stir to combine. Cook for another minute until the sauce has slightly reduced.
Serve. Transfer the bok choy to a platter and garnish with sesame seeds or red pepper flakes, if using. Serve immediately.
