Cook the pasta according to package directions and drain. Return the pasta to the pot.
Meanwhile, in a skillet over medium heat, cook the sausage; drain.
Add the sausage and spaghetti sauce to the pasta and stir to combine. Stir in the Parmesan cheese and half of the pepperoni slices.
Spread pasta mixture into a lightly greased 9-by-13-inch pan. Top with the mozzarella cheese. Arrange remaining half of pepperoni slices over top. Bake for 20 minutes, until cheese is bubbly.