Preheat your oven to 400 degrees F.
Line a large baking sheet with aluminum foil or non-stick cooking paper and set aside.
In a large skillet, heat the olive oil over medium-high heat.
Add the ground beef, salt and pepper and cook for 4-5 minutes or until cooked through.
Add the frozen peppers and onions and cook for an additional 3 to 4 minutes or until all of the moisture has evaporated.
Remove the meat and vegetable mixture from the pan and add it to a large bowl. Allow it to cool for 5 to 10 minutes.
Add all of the cheese to the meat mixture and stir to combine.
Slice the bread horizontally and lay both pieces with the cut side up on the baking sheet.
Spoon the meat mixture on top of the bread, using your hands to mound it evenly and gently press it down.
Bake for approximately 10 - 15 minutes or until all the cheese has melted and the edges of the bread are slightly browned.
Allow it to cool for about five minutes before serving.
Cut into serving size pieces and sprinkle with Italian parsley and extra Parmesan cheese, if desired.