01 - Preheat oven to 375°F. Arrange bell pepper halves in a baking dish with cut side facing up.
02 - Heat 1 tablespoon olive oil in a large skillet over medium-high heat. Add onions and mushrooms; sauté until softened and golden, about 5 to 7 minutes. Add minced garlic and cook for an additional minute. Remove mixture and set aside.
03 - In the same skillet, heat remaining tablespoon of olive oil. Add sliced beef, season with salt and pepper, and cook until just browned, approximately 3 to 4 minutes. Stir in Worcestershire sauce, return the onion and mushroom mixture, toss to combine, then remove from heat.
04 - Place one slice of provolone cheese inside the bottom of each bell pepper half. Fill each with the beef mixture.
05 - Top each stuffed pepper with an additional slice of provolone cheese.
06 - Cover the baking dish with aluminum foil and bake for 25 minutes. Remove foil and continue baking for 5 to 10 minutes more, until cheese is melted and bubbly and peppers are tender.
07 - Allow stuffed peppers to cool for 5 minutes before serving.