I bought some Red Chinese Barbecued Pork a few days ago, it's disappointingly tough. Even sliced very thinly and allowed to simmer for a few minutes in soup, the meat just feels dry and tough. I'm pretty sure it's tenderloin, so there really isn't any fat or collagen to work with. I'd like to make dumplings with it, but only if I can make it seem more tender. Do you know of anything that might work?
It sounds as if you have meat that has been cooked past the point of well done, so that all of the proteins as as contracted and tough as they are going to be, without the couner-veiling benefit of having collagen conversion.
Your only recourse, which may or may not give you results you find acceptable, is to resort to mechanical tenderization. Your best bet is to grind it in the food processor.
Since you mention making dumplings, a healthy portion of cooked cabbage, mushroom, or other vegetables in the filling will also help get a more appropriate texture.