Preheat oven to 375°F (190°C). Slice the bread loaf lengthwise without cutting all the way through and hollow out some of the interior.

In a skillet, heat 1 tablespoon olive oil and sauté the sliced onion and bell peppers until soft and slightly caramelized. Remove and set aside.

In the same skillet, add remaining olive oil and cook the sliced beef until browned. Season with salt and pepper. Return the vegetables to the skillet and mix well.

In a small saucepan, melt butter and stir in minced garlic. Spread this garlic butter mixture inside the hollowed bread loaf.

Line the inside of the loaf with provolone slices. Spoon in the beef and veggie mixture, then top with shredded mozzarella.

Wrap the loaf in foil and bake for 15–20 minutes. Unwrap and broil for 2–3 minutes until the top is golden and crispy.

Slice and serve hot.