Cook spaghetti according to package directions. Meanwhile, crumble sausage into a small skillet; add onion. Cook over medium heat until meat is no longer pink; drain.
Drain spaghetti. Arrange zucchini in a shallow 1-qt. baking dish coated with cooking spray; sprinkle with pepper. Layer with bacon, Parmesan cheese, 1/2 cup spaghetti sauce, spaghetti, remaining sauce, red pepper, sausage mixture, mozzarella cheese and pepperoni.
Sprinkle with herbs. Bake, uncovered, at 350° for 30-35 minutes or until vegetables are tender.