Heat a medium-sized skillet over medium heat and cook the pepperoni until it turns crisp, then transfer to a paper towel-lined plate to drain excess grease.
Spread a very thin layer of pizza sauce on one side of each tortilla, ensuring the coating is light enough that it wouldn’t drip if flipped.
On the sauced side of the bottom tortilla, sprinkle a layer of mozzarella, followed by the crispy pepperoni and any additional toppings like mushrooms or olives. Add another light layer of cheese on top and place a second tortilla over it, sauce side facing inwards.
Warm a cast-iron skillet over medium heat. Place the assembled quesadilla in the skillet and cook for 3–5 minutes per side, or until the tortilla is crisp and the cheese has melted thoroughly.
Remove from the skillet, slice into quarters, and present with a side of pizza sauce for dipping.