Season flour with salt and pepper and dredge chicken breast. Cook in hot oil until brown. Add garlic, mushrooms and continue cooking, shaking pan to redistribute mushrooms. Cook approximately 3 minutes.
Add vinegar, broth, bay leaf and thyme. Cover and cook over medium heat 10 minutes. Transfer chicken to plate, cover with foil. Cook with mushrooms uncovered for 7 minutes. Swirl in butter, discard bay leaf. Pour mushrooms and sauce over chicken. Serve with fettucini.