In large saucepan over medium-high heat, heat oil; add chicken and green pepper. Cook, stirring frequently, until chicken is no longer pink. Add eggplant and zucchini; cook 3 minutes, stirring frequently, or until vegetables are tender. Stir in spaghetti sauce; heat to boiling. Reduce heat; simmer, uncovered, 10 minutes or until chicken is thoroughly cooked. Meanwhile, cook pasta according to package directions. Spoon sauce over hot pasta; sprinkle with Parmesan cheese, if desired.