Slice beef into thin strips. Season with salt, garlic powder and fresh pepper to taste. Heat a large skillet over high heat. When the skillet is very hot, spray with cooking spray and add half of the beef. Cook one minute, then turn steak and cook an additional 30 seconds. Set aside in a large dish.
Spray the skillet again and when it gets hot add the remaining steak, cooking one minute, then turning and cooking 30 seconds more. Add remaining steak to the dish. Return skillet to heat and spray once again with cooking spray; add onions and season with salt and pepper. Cook one minute, then turn and cook onions an additional 30 seconds or until onions are golden.
Lower heat to medium and add ½ tsp olive oil to the skillet, add mushrooms, salt and pepper and lightly spray the top of the mushrooms with cooking spray. Cook 1½ minutes, then turn mushrooms and cook another minute and a half. Add to dish with steak and onions and stir to combine.
Preheat oven to 425° or set your broiler to low.
Once the steak is cooked and ready, cut bread into 4 pieces. Divide steak and mushrooms evenly between four sandwiches and place a slice of cheese on each one. Place sandwiches on a cookie sheet and heat in the oven or broiler until the cheese melts; 2 - 3 minutes, careful not to burn if using the broiler. Enjoy!!
Recipe by The Taste Place at https://www.thetasteplace.com/healthy-cheesesteak-sandwiches-a-football-favorite-with-a-healthy-twist/