Place the sliced onions in the bottom of the slow cooker.
Heat the olive oil in a large heavy skillet over medium-high heat. Season all sides of the beef with the salt and pepper and then add the meat to the hot pan. Brown on both sides, about 3-4 minutes per side. Transfer to the slow cooker, on top of the sliced onion.
Pour the beef broth and Worcestershire sauce over the beef in the slow cooker.
Combine the Italian seasoning, dried thyme, dried oregano, garlic powder and onion powder in a small bowl. Sprinkle evenly over the beef.
Add the chopped pepperoncini and bell pepper to the slow cooker.
Cover and cook on low for 8-10 hours or high for 4-5 hours, until the meat shreds easily with a fork.
Shred the beef. Then continue cooking on high for 20 minutes.
Meanwhile, split the rolls open and place them on a baking sheet, with the inside of the rolls facing up. Broil in the oven for about 2 minutes, until bread is toasted and golden brown, watching the rolls closely so that they don't burn.
Serve shredded Italian beef on top of toasted rolls, topped with a slice of provolone.