Sprinkle both sides of the chuck roast with salt and black pepper.
Heat the oil in a large skillet, then brown all sides of the chuck roast, approx. 5 minutes per side, then transfer the roast to the slow cooker.
Add the sliced onions; then add the beef broth and Worcestershire sauce.
Add the thyme sprigs to the broth.
Cover and set the slow cooker to low for 8 hours.
Remove the chuck roast to a plate and shred using a fork, then place it back into the slow cooker to mix with juices.
Slice the rolls then add the shredded roast beef being careful not to add too much juice or it will become soggy.
Top the sandwich with one or two slices of the provolone cheese.
Place under a broiler for approx. 2-3 min, keep an eye on it until the cheese is melted.
Spoon juices from the crockpot into individual serving bowls, and set alongside the sandwiches.
Dip sandwich into the au jus and enjoy.