Combine first 6 ingredients in a small bowl and set aside. Place chicken between 2 sheets of heavy-duty plastic wrap. Flatten chicken to 1/4" thickness using a meat mallet or rolling pin. Cut each breast into 2" pieces.
Combine flour, salt, and pepper in a small bowl. Dredge ckicken pieces in flour mixture. Heat oil in skillet over medium heat. Add chicken and cook 4 minutes on each side or until done. Remove chicken and keep warm. Stir broth mixture and add to skillet. Cook over medium heat until mixture is thickened and bubbly, stirring constantly. Stir in margarine. Spoon sauce over chicken and sprinkle with parsley, if desired.