Preheat the oven to 400 degrees.
Place the peppers cut side up in a baking dish and season with salt and pepper. Bake for 20 minutes.
While the peppers are baking, prepare the cheesesteak filling. Heat the olive oil in a large pan over medium high heat.
Add the onions to the pan and cook for 4-5 minutes or until onions have softened.
Add the mushrooms and cook for an additional 4-5 minutes until vegetables are browned and tender.
Season with salt and pepper to taste. Season the steak with salt and pepper to taste.
Add the steak to the pan and cook for 3 minutes or until just done.
Fill each pepper with the cheesesteak mixture.
Add a slice of cheese on top of each pepper.
Broil the peppers for 3 minutes or until cheese is golden brown and melted.
Serving Size 6
* Percent Daily Values are based on a 2,000 calorie diet. Your daily value may be higher or lower depending on your calorie needs.