In skillet, heat oil ove medium heat; cook onion, mushrooms, pepperoni, green pepper and oregano, stirring often, for 5 minutes or until onion is softened.
Add tomato sauce, salt and pepper; cook for 3 minutes or until boiling. Meanwhile, in large pot of boiling salted water, cook spaghetti for 8-10 minutes or until tender but firm. Drain well and return to pot. Add sauce; toss to coat well.Servings: 4