Preheat the oven to 210°C.
Clean the chicken and remove the giblets. Pat dry.
Mix sumac, salt and thyme in a small bowl. Add the butter and mix into a paste.
Cut the lemon in half.
Loosen the skin of the chicken over the breast and thighs and rub the spice paste under the skin then all over the chicken. Put half a lemon into the chicken cavity. Tie the legs together with a string.
Place the chicken, breast-side up, on a rack over a roasting tin. Put it in the oven and roast for 20 minutes.
Meanwhile, prepare the vegetables you're using - peel them and cut them into bite-sized chunks. Cut the onion into 8 wedges.
Take the tin out of the oven, transfer the chicken to a plate. Scatter and stir the veggies around in the roasting tin, add the other half the lemon.
Put the chicken (turned over) on the top of the veggies, and roast for another 20 minutes.
Mix the pomegranate molasses with the honey in a small bowl.
Take the roasting tray out from the oven, turn the chicken over once more, so it's breast-side up and stir the vegetables.
Reduce the oven temperature to 180°C.
Season the chick with ground pepper and brush the skin all over with the pomegranate glaze using a silicon brush. Roast for another 20-25 minutes until the chicken is cooked through ( i.e the skin is brown and the juices run clear from the legs).
Transfer the chicken to a plate, cover it with foil and let it rest for 10 minutes.
Carve, then serve with the vegetables and the sauce from the pan. Scatter some pomegranate seeds over it if you like.