Place beef in slow cooker.
In a separate bowl, combine onion soup mix, au jus mix, beef broth & water. Pour over roast.
Cook on low for 6-8 hours.
30 minutes before serving, remove the meat from slow cooker and shred well.
Place the shredded meat back in the juices and let it cook while you prepare the hoagie rolls.
Preheat oven to 450. Slice hoagie rolls in half lengthwise and place them face-up on a baking sheet.
Spread some Dijon mustard on each slice (optional), then add a slice of Provolone cheese.
Toast them in the oven until the cheese is melted.
Remove the rolls from the oven and top the bottom section of each roll with the shredded beef.
Place the top sections over the beef and serve these french dip sandwiches with the reserved juices from the crock pot in small bowls for dipping.