Place chicken between 2 sheets of heavy-duty plastic wrap, and flatten to 1/4-inch thickness using a meat mallet or rolling pin. Cut into 2-inch pieces.
Combine flour, salt, and pepper in a large zip-top plastic bag. Add chicken; seal and shake to coat.
Heat oil in a large nonstick skillet over medium-high heat. Add chicken; cook 4 to 5 minutes on each side or until done. Remove chicken from pan; keep warm.
Combine broth and next 6 ingredients in a small bowl.
Coat pan with cooking spray. Add mushrooms; sauté 3 minutes or until tender. Add broth mixture; bring to a boil. Cook over medium-high heat 4 minutes or until thick, stirring constantly. Stir in butter. Spoon over chicken. Sprinkle with parsley.