Place onion in the bottom of a slow-cooker.

Brush entire roast with mustard. Sprinkle generously with 4-1-1 seasoning.

Sear both sides of seasoned roast in a hot skillet. Place roast atop onions in slow-cooker.

Pour a little bit of the beef stock in the hot skillet. Deglaze the pan by stirring until all the bits are unstuck. Pour over roast in slow-cooker.

Pour in remaining stock.

Add bay leaves and thyme.

Cover and cook on low for 8 hours or until the roast is falling apart tender.

Remove and discard bay leaf and thyme sprigs.

Place the roast on a cutting board. Remove fat. Shred meat and place it back in the slow-cooker to keep warm until ready to serve.

When it's time to eat, remove the onions and meat with a slotted spoon and set aside.

Split open the hoagie rolls and place on a large baking sheet.

Cover the insides of the rolls with cheese slices. Place under a broiler under the cheese melts.

Remove from the oven and add meat and onions to each roll.

Serve each sandwich with a small bowl of the cooking liquid for dipping.