Cook rotini to desired doneness as directed on package. Drain.
Meanwhile, heat oil in large nonstick skillet over medium heat until hot. Add onion; cook and stir 1 to 2 minutes or until crisp-tender. Add sausage and zucchini; mix well. Reduce heat to medium-low; cover and simmer 6 to 8 minutes or until zucchini is tender.
Add tomatoes, salt and pepper; cook 3 to 4 minutes or until thoroughly heated, stirring occasionally. Add cooked rotini; stir gently to mix. Sprinkle with cheese; cover and cook over low heat for 2 to 3 minutes or until cheese is melted.