Preheat the oven to 360°F. Cut thin lines down the potatoes. Use two wooden spoons laid next to the potato as a guide if needed.

Drizzle potatoes with oil and sprinkle with salt and pepper. Bake until the potatoes are fanned out, around 60 minutes.

Fill each slot with a slice of pepperoni, cut in half if needed. Top each potato with pizza sauce and mozzarella cheese.

Bake potatoes for 10 minutes then broil until mozerella is browned and bubbly, around 2 minutes. Sprinkle with parmesan cheese and serve.