Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper for easy cleanup.
Place the bagel halves, cut side up, on the prepared baking sheet.
Optional: For a crispier bagel, toast the bagel halves for 7 minutes
Using a spoon or butter knife, evenly spread about 1-2 tablespoon of pizza sauce on each bagel half.
Sprinkle a pinch of Italian seasoning over the sauce on each bagel.
Generously top each bagel half with shredded mozzarella cheese, making sure to cover the sauce entirely.
Arrange 4-5 pepperoni slices on top of the cheese on each bagel half.
Sprinkle a bit of grated parmesan cheese and a pinch of red pepper flakes (if using) over the pepperoni.
Place the baking sheet in the preheated oven and bake for 8-10 minutes, or until the cheese is melted and bubbly, and the bagels are crispy.
Remove the pizza bagels from the oven and let them cool slightly, Top with more parmesan and red pepper flakes, if desired, before serving. Enjoy them warm!