Preheat the oven to 350°F. Cook the rotini in a large pot of salted water until al dente, then drain well.
In a mixing bowl, combine the drained pasta with the pizza sauce, 1 cup of mozzarella, half the pepperoni slices, the Parmesan, and the Italian seasoning. Stir until everything is evenly coated.
Spread the mixture into a greased 8x8-inch baking dish. Scatter the remaining mozzarella and pepperoni slices over the top.
Bake for 20 to 25 minutes, until the cheese is melted and the edges are bubbling. Let it rest for 5 minutes before serving.