Bring broth to a boil in a small saucepan. Cook for 5 minutes or until reduced to 1 cup. Set aside.
Combine flour, salt, and pepper in plastic Ziploc bag. Add chicken and shake to coat.
Add olive oil to large skillet and place over medium-high heat until hot. Add chicken and cook 5 minutes on each side until browned and cooked through. Remove chicken from skillet and set aside. Add butter to skillet. Place over med-high heat until melted, then add mushrooms and saute until tender. Combine 1 Tbsp. sherry and cornstarch; stir well and set aside.
Add remaining sherry and broth to skillet. Bring to a boil and cook until sauce is reduced to 3/4 cup. Add cornstarch mixture; cook, stirring constantly, about 1 minute or until mixture is thickened. Return chicken to skillet; cover and reduce heat. Simmer 10 minutes. Transfer chicken to a serving platter and top with mushroom mixture. Sprinkle with green onion and parsley.