Pre-heat oven to 400 degrees
Coat pan with extra virgin olive oil. Saute the onions, garlic, & mushrooms (if using) in the oil for 7-9 minutes on medium heat, until lightly browned & tender. Add the Steak-Umms leave in until they are completely cooked.
Place a piece of provolone in the bottom of each pepper. Layer with the steak-umma mixture, filling each pepper to about halfway. Then top the meat with another piece of Provolone and some Mozzarella, fill the pepper with more meat, and then top each stuffed bell pepper with a final piece of provolone and mozzarella.
Bake for 15-20 minutes, or until peppers are cooked through.