Brush your bagel halves with the melted butter mixture and place in the oven, bake for 4-5 minutes, until slightly crispy all over
Remove from oven and place 5 or so slices of pepperoni on each bagel half and sprinkle with Parmesan ( put tomato sauce under the pepperoni if you decide to use it!)
Place back into oven and bake until cheese melts and pepperoni starts to curl around the edges
Let cool for 3-5 minutes, plate with some tomato sauce or ranch dressing