Coat a large saucepan with cooking spray. Heat over medium heat. Add onion, sweet pepper, and garlic; cook until vegetables are tender, stirring occasionally. Stir in undrained tomatoes; tomato sauce; pepperoni; mushrooms, if desired; dried oregano, if using; and, if desired, crushed red pepper. Bring to boiling; reduce heat. Simmer, uncovered, about 10 minutes or until desired consistency, stirring occasionally.
Meanwhile, cook pasta according to package directions; drain. Just before serving, stir in fresh oregano, if using. Serve over hot cooked pasta. Sprinkle with cheese. If desired, garnish with fresh oregano.