Once oil is heated add in onions. Cook for a minute before adding in steak, seasonings, and Worcestershire sauce.
Continue cooking for 3-4 minutes, stirring often, then add in mushrooms. Continue cooking an additional minute or two (lower heat if necessary). Remove from heat.
Take green peppers, cut off 1/2 an inch from the tops to remove the stem, seeds, and membranes. (For a perfectly balanced green pepper, cut a tiny bit off of the bottom so it's even.)
Fill each green pepper with one slice of provolone cheese. Then evenly pack in the cheese steak mixture into each green pepper.
Place stuffed peppers on a baking tray and bake for 40 minutes. Take out the pan and add shredded cheese to each green pepper and return to the oven until cheese is melted and bubbly, about an additional 5 minutes.
Be sure to read the tips in the post on where to buy Philly Cheese steak meat!