Season the cubed chuck roast with salt and pepper.
Optional: Sear the beef in a hot skillet until browned on all sides for extra flavor.
Place the beef into the slow cooker.
Add sliced onions, garlic, Worcestershire sauce, beef broth, and au jus seasoning.
Cover and cook on low for 6 to 8 hours, until the beef is fall-apart tender.
Shred the beef with forks and remove it from the au jus.
Preheat the oven to broil.
Slice the Hawaiian rolls and spread horseradish mayo on the bottom halves.
Layer with shredded beef, onions, and provolone cheese.
Broil for 2 to 3 minutes until the cheese is melted and bubbly.
Add the tops of the buns back on.
Serve warm with au jus drippings for dipping.