In a skillet over medium heat, heat olive oil and add onions and peppers. Cook until peppers are soft enough to stick your knife into without resistance. Add mushrooms and chopped, grilled rib eye. Add salt and pepper to taste.
Turn heat to high and separate into four portions. Break up cheese slices and place equal amount on each portion. Fold cheese into portions until it is melted.
Prepare bread by cutting loaf into quarters. With your hands, gut the quarters, leaving about half of the bread adhered to the crust.
In the oven, toast the quarters for 2 minutes on a baking sheet. (Adding butter and fresh garlic to this adds a lot of great flavor.)
When bread is toasted to your liking, remove from the oven and fill each quarter with one of the portions in the pan.