Place pork roast in 3 1/2- to 6-quart slow cooker. Arrange onion on top. In small bowl, combine all remaining ingredients except tortillas; mix well. Pour over pork.
Cover; cook on low setting for 8 to 10 hours.
Remove pork from slow cooker; place on large plate. With 2 forks, pull pork into shreds. Pour sauce from slow cooker into bowl; stir in pork. Spoon pork mixture onto each tortilla; roll up.