Prepare the bok choy: Trim the tough ends, slice each baby bok choy in half lengthwise, rinse well between the stems, then pat dry.
Mix the sauce: In a small bowl, stir together soy sauce, water or broth, sesame oil, and rice vinegar or lemon juice. Add cornstarch if you want a thicker sauce.
Cook the aromatics: Heat oil in a large skillet or wok over medium-high heat. Add garlic and ginger, then stir for about 30 seconds until fragrant.
Sear the bok choy: Place bok choy cut side down in the pan. Cook for about 2 minutes, without moving too much, until lightly seared.
Steam briefly: Flip the bok choy, pour in the sauce, cover, and steam for 1–3 minutes until the stems are crisp-tender and the leaves are bright green.
Finish and serve: Uncover, toss gently in the sauce, and cook 30 seconds more if needed. Top with sesame seeds and scallions, then serve hot.
