Bok choy isn't too hard to cook traditionally, but with sous vide it can be tenderized without making it overly soft. It also completely eliminates the cleanup since you don't have to pull out a pot or pan. If you prefer a thicker sauce you can always reduce it on the stove after the sous vide process is complete.
Preheat the water bath to 183°F (83.9°C).
Combine all ingredients in a bowl and toss to mix well. Pour into a sous vide bag and arrange in a single layer. Seal the bag then place in the water bath and cook for 15 to 30 minutes.
Once the bok choy is tender remove it from the water bath.
Remove the bok choy from the sous vide bag and place in a bowl. Drizzle with some fish sauce and sesame oil. Sprinkle with the sesame seeds then serve.