Heat the oven to 375°F. Cook the pasta until just tender, then drain it.
Brown the sausage in a large skillet, breaking it into small pieces. Drain excess grease.
Stir in the marinara and Italian seasoning. Add the pasta and mix until coated.
Spread half the mixture in a greased 9-by-13-inch baking dish. Sprinkle with 1 cup mozzarella, then add the remaining pasta.
Top with the rest of the mozzarella, pepperoni, and Parmesan.
Bake for 20 minutes, until the cheese melts and the edges bubble. Let it rest for five minutes so nobody burns their tongue in the name of enthusiasm.