Start by seasoning the beef chuck roast with salt and pepper.
In a skillet over medium-high heat, add olive oil. Once heated, sear the beef on all sides until browned, about 3-4 minutes per side.
Transfer the seared roast to the slow cooker.
In the same skillet, add the sliced onion and sauté for 2-3 minutes until softened. Add the minced garlic and cook for an additional minute until fragrant.
Pour in the beef broth, add the Italian seasoning, dried oregano, crushed red pepper flakes (if using), and juice from the jar of pepperoncini peppers. Stir to combine.
Pour this mixture over the beef in the slow cooker, then add the pepperoncini peppers on top.
Cover and cook on low for 8 hours or on high for 4 hours, until the beef is tender and easily shreds with a fork.
Once cooked, remove the beef from the slow cooker and shred it using two forks. Return the shredded beef to the slow cooker, stirring it to combine with the juices.
Serve the Italian beef on hoagie rolls or crusty bread, topped with provolone cheese if desired.