Place the thinly sliced beef in the slow cooker. Add the sliced onion, green bell pepper, mushrooms, and minced garlic on top.
In a small bowl, mix together the beef broth, worcestershire sauce, italian seasoning, salt, and black pepper. Pour this mixture over the beef and vegetables.
Give everything a gentle toss to combine. Cover and cook on low for 6 to 7 hours or on high for 3 to 4 hours, until the beef is very tender and the vegetables are soft.
Stir the mixture well and use a slotted spoon to drain some of the excess liquid when scooping. The filling should be juicy but not watery.
Split the hoagie rolls open and pile them high with the Philly cheesesteak filling. Top each sandwich with a slice of provolone cheese.
Place the open sandwiches under the broiler for 1 to 2 minutes until the cheese is perfectly melted and bubbly and the edges of the rolls are lightly toasted.
Serve immediately while hot. These are incredible alongside a side of seasoned fries or a simple side salad.