01 - Preheat your oven to 400°F. Arrange bell pepper halves cut side up in a baking dish.
02 - Heat 1 tablespoon olive oil in a large skillet over medium heat. Add onions and mushrooms; sauté for 5–6 minutes until softened. Add garlic and cook 1 minute more.
03 - Push the vegetables to the side of the skillet. Add remaining olive oil and the sliced beef. Sauté for 3–4 minutes, stirring, until just cooked. Stir in Worcestershire sauce, salt, and pepper. Mix beef and vegetables together, then remove from heat.
04 - Place one slice of provolone cheese into the bottom of each pepper half.
05 - Evenly fill each pepper with the beef and vegetable mixture. Top with another slice of provolone.
06 - Cover the baking dish with foil and bake for 20 minutes. Remove foil and bake for an additional 10–15 minutes, until the peppers are tender and cheese is melted and slightly golden.
07 - Serve hot, garnished with chopped fresh parsley if desired.