Combine butter and sumac in a small bowl. Rub sumac butter all over the outside of the chicken; season. Tie the chicken legs together with kitchen string; place in a large roasting pan. Wrap beetroot individually in foil; add to pan with chicken. Roast for 30 minutes.
Baste chicken with pan juices. Toss carrots in oil; season and add to pan. Roast for a further 35 minutes or until chicken is cooked through and the skin is golden brown. Cover chicken loosely with foil; stand for 10 minutes.
Meanwhile, peel beetroot and cut in half. Return beetroot to pan.
Serve roast chicken and vegetables with mint, fetta and dukkah.