Heat spaghetti sauce in small saucepan over low heat until thoroughly heated. Cover to keep warm.
Meanwhile, place 1 chicken breast half, boned side up, between 2 pieces of plastic wrap or waxed paper. Working from center, gently pound chicken with flat side of meat mallet or rolling pin until about 1/4 inch thick; remove wrap. Repeat with remaining chicken breast halves.
In shallow bowl, combine bread crumbs, Parmesan cheese and margarine; mix well. Add chicken breast halves; turn to coat.
Spray large nonstick skillet with nonstick cooking spray. Heat over medium-high heat until hot. Add chicken; cook 4 to 6 minutes or until fork-tender and juices run clear, turning once.
To serve, place cooked chicken on serving platter; sprinkle with shredded cheese. Pour warm spaghetti sauce over chicken; sprinkle with parsley.