Preheat oven to 375°F (190°C) and line a baking sheet with parchment paper.
Cut a rectangular opening in the top of the bread loaf and hollow out the center, leaving a 1-inch thick shell on all sides.
Heat 1 tablespoon of olive oil in a large skillet over medium-high heat.
Sauté the onion and green bell pepper until softened and slightly caramelized, then remove from skillet and set aside.
Add the remaining tablespoon of olive oil to the same skillet and sear the steak slices until browned and fully cooked.
Season the steak with salt and pepper, then stir the sautéed vegetables back into the meat mixture.
Place 4 slices of provolone cheese into the bottom of the hollowed bread loaf.
Pack the steak and vegetable mixture tightly into the bread shell.
Top the filling with the remaining 4 provolone cheese slices.
Combine melted butter and garlic powder in a small bowl and brush the mixture over the exterior of the bread loaf.
Bake for 12 to 15 minutes or until the cheese is melted and the bread is golden brown.
Let rest for 5 minutes before slicing into sections and serving.