Preheat oven to 375°F (190°C) and grease a 9x5 inch loaf pan.
Heat olive oil in a skillet over medium heat and sauté the bell pepper, onion, and mushrooms for 5-7 minutes until softened. Allow to cool slightly.
In a large mixing bowl, combine the ground beef, breadcrumbs, eggs, Worcestershire sauce, salt, pepper, garlic powder, and the sautéed vegetable mixture.
Press half of the meat mixture into the bottom of the prepared loaf pan.
Layer 4 slices of provolone cheese over the first layer of meat.
Top with the remaining meat mixture, pressing down firmly and sealing the edges to enclose the cheese.
Bake for 50 minutes.
Place the remaining 4 slices of provolone cheese on top of the loaf and bake for an additional 10 minutes or until the internal temperature reaches 160°F (71°C).
Remove from oven and let the meatloaf rest for 10 minutes before slicing and serving.