Season the chuck roast with salt, pepper, oregano, basil, garlic powder, onion powder, and red pepper flakes.
Place the seasoned beef in a slow cooker.
Pour the beef broth and sliced pepperoncini over the meat.
Cover and cook on low for 8 hours or high for 4–5 hours, until the beef is tender and shreds easily.
Preheat the oven to 300°F (150°C).
Place the beef in a Dutch oven, pour in the broth and pepperoncini, and cover.
Cook for 3 hours, checking occasionally and adding more broth if needed.
Remove the beef from the slow cooker or oven and shred it using two forks.
Return the shredded beef to the broth and let it soak for another 10–15 minutes.
Preheat the oven to 375°F (190°C).
Slice the hoagie rolls and spread a little butter on each.
Toast them for 5 minutes until slightly crispy.
Pile the shredded beef onto the toasted rolls.
Spoon some of the au jus over the top.
Add sliced pepperoncini and giardiniera if using.
Serve hot with extra au jus on the side for dipping.