1. Preheat your oven to 375°F (190°C). Cut the tops off the bell peppers and remove the seeds and membranes. Place them in a baking dish, cut side up.
2. In a large skillet, heat olive oil over medium-high heat. Add the sliced onion and mushrooms, sautéing until they start to soften, about 5 minutes.
3. Add the thinly sliced beef to the skillet, cooking until browned. Stir in the garlic powder, salt, and pepper, mixing well.
4. Pour in the beef broth and Worcestershire sauce, allowing the mixture to simmer for about 2-3 minutes, until slightly thickened.
5. Place a slice of provolone cheese at the bottom of each bell pepper. Fill each pepper with the beef mixture, then top each with another slice of cheese.
6. Cover the baking dish with foil and bake for 20 minutes. Remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden.

Here’s a tip from my kitchen: If you’re in a pinch for time, you can prep the filling the night before. Just store it in the fridge and assemble your peppers when you’re ready to bake!