In a skillet, add some oil and mushroom. Let the mushrooms cook on high heat until their color changes. Add the onions and saute them with the mushrooms. Now, remove the veggies and add the steak.
As soon as the steak changes color, drain it. Add the veggies back to the skillet, salt, and pepper.
Start placing the cheese slice at the bottom of the beef and cover it with more cheese slices. Repeat the process for the other two peppers and bake them at 400 degrees F for 25-30 minutes.
