In a small bowl combine the butter, Chicken Rub, lemon zest and thyme.
Spread most of the mixture evenly over the chicken on all sides, then spread the remaining rub under the chicken skin over each side of the breast.
Stuff the cavity of the chicken with the carrot, onion, celery and lemon.
Season the chicken lightly on all sides with salt and pepper, then transfer to a roasting pan or aluminum-foil-lined pan; cook until golden brown and a thermometer inserted into the thigh registers 165 degrees, about 1 ½ hours.
Set aside to rest for at least 10 minutes before carving.