Coat a 10-inch skillet with nonstick vegetable spray. Heat over medium heat. When hot, add chicken and cook until light brown, about 3 minutes on each side. Transfer chicken to a plate. Add olive oil to pan, sauté garlic and mushrooms briefly, being careful not to burn garlic. Return chicken to pan, add vinegar, chicken broth, thyme and pepper. Reduce heat, cover and simmer for 15 minutes or until chicken is cooked. Juices will run clear when meat is pierced in its thickest part with a fork. Transfer to serving dish and top chicken with mushrooms and pan sauce. Sprinkle with chopped parsley.