Cook pasta according to manufacturer's directions, al dente. Drain and set aside. Set pasta pot aside also.

Preheat oven to 350 degrees.

In a large nonstick skillet, cook pepperoni over medium heat for about 3-4 minutes or until lightly browned. Remove to a paper towel with a slotted spoon. In the fat remaining in the pan, cook the onion for 2 or 3 minutes or until soft. Add the tomatoes, tomato sauce, Worcestershire sauce, oregano, basil and some pepper. Bring to a boil and simmer, uncovered, for about 10 minutes. Stir occasionally.

Put the butter in the pasta pan, heat on low, and swirl it until it melts. Add pasta and toss until well-coated. Add Parmesan and toss again to coat. Place pasta in a large shallow casserole which has been sprayed with nonstick cooking spray. Pour sauce over pasta, top with the pepperoni, then mozzarella. Bake for 25 to 30 minutes or until heated through and the mozzarella is melted. Serve immediately.