We're partial to homemade pizza sauce around here, but any store-bought sauce will do the trick if you want to save a little extra time.
Both shredded or sliced mozzarella cheese work for this recipe. Shredding the cheese straight from the block is your best bet to make it extra melty and delicious.
Instead of pepperoni, or in addition to, you can easily use pizza sausage. Green peppers, mushrooms, onions, olives, or just about any of your favorite pizza toppings can also be incorporated! If you plan on adding vegetables I would recommend quickly sauteeing them before adding them to the sliders to be sure they are cooked through when coming out of the oven. The same goes for the sausage, crumble and cook partially before adding to ensure doneness.