01 - Set the oven to 375°F to prepare for roasting the peppers.
02 - Arrange bell pepper halves cut-side up in a large baking dish and roast for 10 minutes to start softening.
03 - Heat olive oil in a large skillet over medium-high heat. Add onions and optional mushrooms, sautéing until softened, about 5 minutes.
04 - Stir in minced garlic and cook for 1 minute until fragrant.
05 - Add thinly sliced beef to the skillet. Season with salt, pepper, and Worcestershire sauce. Cook, stirring, until beef is just cooked through, 3 to 4 minutes.
06 - If desired, stir in softened cream cheese until melted and fully incorporated. Remove skillet from heat.
07 - Remove peppers from the oven and evenly spoon the beef mixture into each pepper half.
08 - Place one slice of provolone cheese on top of each stuffed pepper.
09 - Return stuffed peppers to the oven and bake for 15 to 20 minutes until cheese melts and peppers become tender.
10 - Remove from oven and serve immediately while hot.