Preheat oven to 375 degrees.
Cut the peppers in half, cleaning out the seeds and ribs.
Position on a baking sheet with the cut side of the pepper facing up.
Brush the sauce inside each pepper half, coating well.
Sprinkle half the pepperoni inside each pepper, sprinkle with half the red pepper flakes, and half the basil.
Add the mozzarella cheese to each pepper and top with the balance of the pepperoni, red pepper flakes, and basil.
Bake for 20 - 25 minutes in the oven, until golden brown.
Add additional red pepper flakes or basil to taste.