Preheat your oven to 375°F. Line a baking sheet with parchment paper.
Slice each croissant in half lengthwise to create a top and bottom.
On the bottom half of each croissant, sprinkle half of the shredded mozzarella cheese evenly.
Layer the pepperoni slices over the cheese, then sprinkle with Italian seasoning, garlic powder, and crushed red pepper flakes if using.
Top with the remaining mozzarella cheese and place the top half of the croissant back on.
Brush the tops of the croissants with olive oil and sprinkle with grated Parmesan cheese.
Place the croissants on the prepared baking sheet and bake for 12-15 minutes, or until the cheese is melted and the croissants are golden brown.
Remove from the oven and let cool for a few minutes before serving.