Prepare the Ingredients:
Slice the beef, onions, bell peppers, and mushrooms (if using). Mince the garlic and shred the provolone cheese.
Cook the Tortellini:
Boil tortellini in salted water according to package instructions, drain, and set aside with a drizzle of olive oil.
Make the Cheesesteak Filling:
Heat olive oil in a skillet, sear the beef until browned, and remove. Sauté onions, peppers, and mushrooms until caramelized, then add garlic and return the beef to the skillet. Season with salt and pepper.
Craft the Provolone Sauce:
Melt butter in a saucepan, whisk in flour to make a roux, and gradually whisk in milk or cream. Stir until thickened, then add provolone and a pinch of nutmeg. Stir until the cheese melts completely.
Combine and Serve:
Toss the tortellini with the cheesesteak filling, pour the provolone sauce over, and mix gently. Serve hot, garnished with parsley.