01 - Preheat 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 5–6 minutes until softened. Add garlic and cook 1 minute more.
03 - Push vegetables to the side of the skillet. Add remaining olive oil and sliced beef. Sauté 3–4 minutes, stirring, until just cooked. Stir in Worcestershire sauce, salt, and pepper. Combine beef and vegetables, then remove from heat.
04 - Place one slice provolone cheese in the bottom of each pepper half. Evenly fill peppers with beef mixture. Top with another slice provolone.
05 - Cover baking dish with foil and bake 20 minutes. Remove foil and bake 10–15 minutes more until peppers are tender and cheese is melted and golden.