In a large nonstick sauté pan, heat 2 tablespoons olive oil on medium-high heat. Cook mushrooms, stirring occasionally, until tender. Remove from pan, and set aside.

Season chicken breasts on both sides with garlic salt and black pepper. Dredge in flour, shaking off excess. In same pan, heat remaining 1/4 cup olive oil on medium-high heat. Cook chicken breasts, in batches, 3 to 5 minutes on each side, or until golden brown. (If browning too quickly, reduce heat to medium, and add oil if needed.) Remove chicken from pan; set aside.

Deglaze pan with wine, using a wire whisk and stirring briskly to loosen brown bits from bottom of pan. Cook for 1 to 2 minutes, stirring constantly. Add chicken stock and butter, whisking to combine. Return chicken and mushrooms to pan, and cook until heated through. Garnish with chopped parsley, if desired.