Place turkey breast in a shallow baking pan; coat the outside of the turkey with cooking spray or lightly rub with vegetable oil. Tuck onion and celery underneath in the breast cavity. Combine seasonings and salt; rub over turkey.
Bake, uncovered, for 2-1/2 to 3 hours or until a meat thermometer reads 185°, basting every 30 minutes. Remove turkey and keep warm. For gravy, combine flour and water in a saucepan until smooth. Add pan drippings and bouillon. Bring to a boil over medium heat, stirring constantly; boil for 2 minutes.
Note: If the bottom of the pan begins to dry, add a slight amount of water to the pan.