Pepperoni Pizza Casserole

8 ounces (about 3 cups) uncooked spiral pasta
1 pound Italian sausage (casings removed) or ground beef  
4 cups spaghetti sauce
1 (4-ounce) can mushrooms, drained
1 cup grated Parmesan cheese
1 (6-ounce) package sliced pepperoni
8 ounces shredded mozzarella cheese

1. Preheat the oven to 350 degrees. On the stovetop, bring a large pot of water to a boil. Cook the pasta according to package directions and drain. Return the pasta to the pot.
2. Meanwhile, in a saute pan over medium heat, cook the sausage; drain. Add the sausage, spaghetti sauce and mushrooms to the pasta and stir to combine. Stir in the Parmesan cheese and half the pepperoni slices.
3. 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.