In a large resealable plastic bag, combine the flour, onion powder and mustard.
Add pork, one portion at a time, and shake to coat.
In a large skillet, brown pork in oil on all sides.
Transfer to a 5-qt. slow cooker. Pour broth over pork.
Cover and cook on low for 5-6 hours or until tender.
Remove pork and keep warm.
Let pork stand for 10-15 minutes before slicing.
Strain cooking juices, reserving 2-½ cups juices; skim fat from reserved juices. Transfer to a small saucepan. Bring liquid to a boil. Combine cornstarch and water until smooth; gradually stir into the pan. Bring to a boil; cook and stir for 2 minutes or until thickened. Serve with gravy and mashed potatoes if desired.