Preheat oven to 350 degrees. Prepare the pasta as directed on the package.
While the pasta is cooking, place a large skillet over medium high heat on the stove top. Warm up the olive oil in the skillet and then add the onions and green pepper.
Cook for a few minutes until vegetables are tender, then add the mushrooms and garlic. Cook for 1 more minute. Push everything to the side of the pan and add the sausage.
Cook the sausage, breaking it into small pieces as it cooks. Cook until it's no longer pink. Drain grease. Add in the pepperoni slices and stir together.
Add in remaining ingredients to the skillet except for Mozzarella cheese.
Turn the heat down to medium and let the mixture simmer for 2-3 minutes so that the flavors can meld together.
Turn off the heat and add the cooked pasta to the skillet pan. Mix everything together.
Spray a large 9 x 13 inch baking pan with non-stick cooking spray.
Dump the pasta mixture into the pan. Top with Mozzarella cheese and any other toppings you prefer.
Bake in the oven (uncovered) for about 30 minutes or until cheese is melted and pasta is heated through.