Preheat your oven to 375°F (190°C).
Line a baking sheet with parchment paper.
Slice the Italian bread in half lengthwise, creating two long pieces.
In a mixing bowl, combine the mozzarella, provolone, and Parmesan cheeses. Set aside.
In a small bowl, mix the olive oil, garlic powder, Italian seasoning, and red pepper flakes (if using).
Brush the cut sides of the bread with the olive oil mixture using a butter knife or spatula.
Evenly distribute the cheese mixture over the brushed bread halves.
Place the bread halves on the prepared baking sheet, cut side up.
Bake in the preheated oven for 15-20 minutes or until the cheese is melted and bubbly, and the edges of the bread are golden brown.
Remove from the oven and let cool for a few minutes. Slice into 8 pieces.
Garnish with fresh parsley if desired and serve warm.