I agree with what @KennethT said about par-boiling before the saute.
I never worked in a Chinese kitchen but books by Chinese professional chefs regularly use this method.
The same sources also say that Chinese chef's don't sear the meat to burn off meat scum so that's why the par-boiling is necessary in many cases - like a stock or braise.
I was never sure myself the need to par-boil choy-sum or other delicate vegetables (but the method applies here also)
but when I do so, I notice the veg has more gloss, moisture, and suppleness than direct heat sear (with a tablespoon of water or too to make it cook through if necessary)
@jemartin - the recipe you have sort of reminds me of maipo tofu (which you might want to try but I'm guessing you already know - one of the super popular dishes of Sichuan)
