Pat the beef chuck roast dry with paper towels. Season all sides with salt and black pepper.
Heat olive oil in a large skillet over medium-high heat. Sear the beef roast on all sides until browned, about 3-4 minutes per side.
Transfer the seared beef roast to the slow cooker.
In a medium bowl, combine beef broth, water, Worcestershire sauce, dried Italian seasoning, garlic powder, onion powder, crushed red pepper flakes, and minced garlic. Stir well.
Pour the broth mixture over the beef in the slow cooker.
Add the sliced green bell pepper and onion on top of the beef.
Cover and cook on low for 8 hours, or until the beef is very tender and shreds easily.
Remove the beef from the slow cooker and shred it using two forks.
Return the shredded beef to the slow cooker and stir to combine with the cooking juices and vegetables.
To serve, split the Italian sandwich rolls and fill each with a generous portion of the shredded beef mixture. Optionally, dip the sandwiches in the cooking juices for extra flavor.