Making Sheet Pan Philly Cheesesteak is straightforward and can be done in just a few steps:

1. Preheat the Oven: Start by preheating your oven to 400°F (200°C).
2. Prepare the Vegetables: On a large sheet pan, place the sliced onions, bell peppers, and mushrooms (if using).
3. Season the Vegetables: Drizzle the olive oil over the vegetables. Sprinkle with garlic powder, salt, and pepper. Toss everything together to coat evenly.
4. Add the Beef: Arrange the thinly sliced beef on top of the vegetables. Season with additional salt and pepper.
5. Bake: Place the sheet pan in the preheated oven and bake for 15-20 minutes, or until the beef is cooked through and the vegetables are tender.
6. Add Cheese: Remove the pan from the oven. Lay slices of provolone cheese evenly over the beef and return it to the oven for 5 minutes or until the cheese is melted and bubbly.
7. Serve: Once the cheese is melted, take the pan out of the oven. Use a spatula to serve the beef and vegetable mixture on hoagie rolls or plates, garnishing with fresh parsley if desired.

Follow these simple steps, and you’ll have a delicious Sheet Pan Philly Cheesesteak ready to enjoy in no time!