This step is optional but adds great flavor. In a hot pan with a little oil, brown both sides of he pot roast really well. Don't cook it all the way through, just brown each side in the hot skillet.
Put beef roast in slow cooker.
In a medium bowl, combine beef broth, onion soup mix, au jus seasoning and water and stir until combined.
Pour mixture over beef, put cover on slow cooker and cook on low for about 8 hours.
An hour before serving, shred meat with two forks or take it out and slice thinly.
Place meat back in the slow cooker for another hour.
When ready to serve, place several slices of beef on roll, add sliced mozzarella cheese and place under the broiler (or use broil option on toaster oven). Watch carefully, broil for just a couple of minutes until cheese is melted and roll is just slightly toasted.
Serve sandwich with a bit of Au Jus from the slow cooker (you may want to strain it first).
Optional toppings include onions, green peppers and mushrooms.
We also enjoy adding some mayonnaise to our buns.
Also, instead of the water, you can substitute with more beef stock if you like.