01 - Scatter the thinly sliced onion and minced garlic evenly across the bottom of the slow cooker insert.
02 - Combine the kosher salt, black pepper, dried Italian seasoning, basil, and oregano in a small bowl. Rub the seasoning mixture over all surfaces of the chuck roast, pressing gently to adhere.
03 - Place the seasoned roast on top of the onion and garlic bed in the slow cooker.
04 - Pour the beef broth and pepperoncini juice over and around the roast. Sprinkle with crushed red pepper flakes if using.
05 - Cover the slow cooker and cook on LOW for 8 hours or on HIGH for 5 to 6 hours, until the beef is fork-tender and pulls apart effortlessly.
06 - Transfer the roast to a large cutting board. Using two forks, shred the meat, discarding any large pieces of excess fat. Return the shredded beef to the slow cooker and toss thoroughly in the accumulated juices.
07 - If desired, spread softened butter on the cut sides of each roll and toast under the broiler until golden brown, about 1 to 2 minutes.
08 - Mound the shredded beef generously onto each roll. Layer two slices of provolone cheese on top and finish with a handful of sliced pepperoncini.
09 - For a melted cheese finish, place the assembled sandwiches under the broiler for 1 to 2 minutes until the provolone is bubbly and golden. Serve immediately while warm.