In a large frying pan over high heat, add olive oil and heat so that a drop of water will sizzle when you drop it in the oil.

Lower heat to medium, and add onions, mushrooms and green pepper, stir and cook until mushrooms darken and onions start to look transparent.

Add steak slices and cook for approximately 3 minutes or until meat is lightly browned.

Add salt and pepper to taste.

Heap cooked meat mixture in a long length-wise pile across the pan, lay cheese slices over meat until melted.

Slice bread lengthwise. Using a spatula, scoop 1/2 the meat mixture and cheese and lay on bread with cheese on top.