Place all of the ingredients except the pepperoni and the cheese in the Instant Pot. Make sure the noodles are covered in the liquid but do not stir.
Put the lid on the Instant Pot and pressure cook on HIGH for 8 minutes. When the timer finishes, perform a Quick Release.
Open the lid of the Instant Pot and stir. Mix in ½ cup mozzarella and ½ of the pepperoni, and stir again until the cheese is melted.
Sprinkle the rest of the mozzarella and pepperoni on top of the pasta. Close the lid and turn to keep warm for 2 minutes until the cheese on top melts. Enjoy!