Preheat the oven to 375°F. Line a baking sheet with parchment paper.
Slice each croissant in half lengthwise to create a top and bottom.
In a bowl, combine the shredded mozzarella cheese, pepperoni slices, Italian seasoning, garlic powder, and black pepper. Mix well.
Spoon the cheese and pepperoni mixture evenly onto the bottom half of each croissant.
Place the top half of the croissant back on and gently press down.
Brush the tops of the croissants with olive oil for a golden finish.
Place the filled 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 with marinara sauce for dipping.