Combine plum sauce, pineapple juice, soy sauce and ginger; pour over pork in large plastic food storage bag. Press air out of bag; close top securely. Turn bag over several times to coat pork well. Refrigerate 1 hour, turning over once.
Bake pork at 400 degrees F 35 minutes, or until meat thermometer inserted into thickest part registers 155 degrees F. Let stand 5 minutes. Slice and serve with additional plum sauce.