Trim the root ends off the bok choy and halve each head lengthwise (quarter any large heads). Rinse well between the leaves to get rid of grit, then pat dry with a towel.
Whisk the soy sauce, rice vinegar, honey, and water together in a small bowl. Set the sauce aside.
Heat 1.5 tbsp avocado oil in a 12-inch (30 cm) skillet or wok over high heat until it shimmers.
Lay half the bok choy cut side down in a single layer, without crowding the pan. Sear for 2 to 3 minutes until the cut sides are charred golden in spots.
Add half the garlic and ginger to the pan and cook for 30 seconds until fragrant. Pour in half the sauce, cover, and steam for 2 minutes until the stalks are crisp-tender and the leaves are wilted bright green. Transfer to a plate.
Wipe the pan if needed, add the remaining 1.5 tbsp avocado oil, and repeat the searing and steaming process with the second batch of bok choy, garlic, ginger, and sauce.
Return all the bok choy to the pan and toss together. Turn off the heat and drizzle in the toasted sesame oil, tossing to coat.
Sprinkle with sesame seeds, scallions, and red pepper flakes if using. Serve right away while the stalks still have some crunch.