Preheat oven to 350 degrees.

Bring a large pot of water to boil. Season liberally with salt, about 1 tablespoon. Cook pasta for 6-7 minutes. Strain. Pasta will be firm.

In a large skillet brown Italian sausage, about 5 minutes. Strain.

In the same pan you cooked the sausage stir together bell pepper, red onion, mushrooms and pepperoni. Cook for 3-4 minutes or until vegetables soften. Return sausage to pan. Stir to combine. Add in pasta and pizza sauce. Mix well. Remove from heat.

To bake one casserole: Place half of the casserole mixture into a 8" x 8" glass casserole dish. Sprinkle 1 1/2 cups of shredded mozzarella cheese on top. Bake for 15 minutes. Remove. Top 1/2 cup shredded mozzarella and 1/4 cup Parmesan cheese. Place under the broiler for 1-2 minutes or until cheese starts to brown. Serve immediately.

To freeze one casserole. Line a 8" x 8" casserole dish with foil, making sure to leave enough hanging off the sides to wrap around the casserole.Spoon remaining half of casserole mixture into prepared pan. Set pan on top of ice water to cool rapidly. Then freeze for a couple of hours or until firm. Lift the frozen casserole out of the dish, wrap in foil and place in a plastic freezer bag. Cook within 2-3 months.

When ready to bake, place frozen casserole in casserole dish and thaw in the refrigerator for 24 hours.

Preheat oven to 350 degrees. Unwrap the casserole. Sprinkle 1 1/2 cups of shredded mozzarella cheese on top and bake for 20-25 minutes or until mozzarella is melted and casserole is heated through. Remove from oven sprinkle 1/2 cup shredded mozzarella and 1/4 shredded Parmesan on top. Place under the broiler for 1-2 minutes or until the cheese starts to brown.

Serve immediately.