Place chicken between 2 sheets of heavy-duty plastic wrap; pound each piece to 1/2-inch thickness using a meat mallet or rolling pin. Sprinkle both sides of chicken evenly with salt and pepper. Place flour in a shallow dish. Dredge chicken in flour, turning to coat; shake off excess flour.
Heat olive oil in a large skillet over medium-high heat. Add chicken; cook 3 minutes on each side or until browned. Remove chicken from pan; keep warm. Add mushrooms, wine, broth, and juice to pan; reduce heat, and simmer 10 minutes or until mixture is reduced to 2/3 cup. Return chicken to pan, turning to coat well. Cover and cook 5 minutes or until chicken is done. Sprinkle with parsley.

Note:
If you do not care to use the marsala, you can replace it with 1/2 cup of additional chicken broth. Without the marsala, the flavor won't be exactly the same, but the recipe will work just fine.