1 hour ago, weedy said:I'd wonder if they are velveting it
but I might add that if they BOIL the sauce and then put in the chicken in some reasonable time frame after boring, it's bound to be a lot hotter than 140f in there.
140F chicken has an almost rubbery texture that not everyone likes.
To get a more "traditional", falling apart, kind of texture you need to go 150-160.
http://www.seriouseats.com/2014/07/chinese-velveting-101-introduction-water-velveting.html
I would contest the "velveting". Soy sauce chicken (breast) is cooked as a whole, not in slices, so both marinate penetration and short velveting times do not apply. It is - by all standards - a regular poaching process.
I agree on the textural part. 140 F is "undercooked" count compared what the OP asks for. The classical process starts at higher temperatures, so at least the outside of the breast will have a firmer texture.
I would run a series of SV temperatures to find the texture you like. I also think that rapid chilling is detrimental to the texture and it will pronounce any "stringyness", so a slower cooling would enhance the uniform structure you are looking for ... Please let us know your findings !