Mix the first 5 ingredients in a small bowl. Place vegetables in a 6- or 7-qt. slow cooker; top with turkey. Rub turkey with seasoning mixture., Cook, covered, on low until a thermometer inserted in turkey reads at least 170°, 5-6 hours. Remove from slow cooker; let stand, covered, 15 minutes before slicing., Meanwhile, strain cooking juices into a small saucepan. Mix flour and water until smooth; stir into cooking juices. Bring to a boil; cook and stir until thickened, 1-2 minutes. Serve with turkey.