Wash the bok choy thoroughly and chop it into bite-sized pieces, separating the stems from the leaves. Mince the garlic.

Heat the sesame oil in a wok or large skillet over medium-high heat. Add the minced garlic and sauté for about 30 seconds, or until fragrant.

Add the bok choy stems to the wok and stir-fry for 2-3 minutes, until they begin to soften.

Add the bok choy leaves and continue to stir-fry for another 2-3 minutes, until the leaves are wilted but still vibrant green.

In a small bowl, whisk together the soy sauce, rice vinegar, and red pepper flakes (if using). Pour the sauce over the bok choy and stir well to combine.

Pour in the cornstarch slurry (cornstarch mixed with water) and stir continuously until the sauce thickens slightly.

Remove from heat and transfer the bok choy to a serving dish. Garnish with toasted sesame seeds and sliced green onions. Serve immediately.