Pour the entire jar of pepperoncini peppers, along with all of their juice, over the top of the meat. You can leave the peppers whole or slice some if you like them mixed into the meat.
Cover the slow cooker and cook on LOW for 7–8 hours, or on HIGH for about 4 hours, until the beef is very tender and shreds easily with a fork.
Once tender, use two forks to gently shred the beef right in the slow cooker, mixing it well with the cooking juices and peppers. Taste and adjust seasoning if needed (the mix and peppers usually provide enough salt).
Split the hoagie or Italian rolls and, if desired, lightly toast them under the broiler or in a skillet until just crisp and warm.
Pile the hot Italian beef onto the rolls, spooning a bit of the juice over the meat if you like a wetter sandwich. Add some of the cooked pepperoncini on top for extra tang and heat.
