Halve the lemons lengthways and squeeze all the juice into a jug. Pull the pulp from each lemon half to leave a shell. Discard the pulp. Cut a thin slice off the base of each lemon so it will stand firmly when upturned. Set aside.
Place the couscous in a bowl. Add 1/3 cup lemon juice, the spices, 3 cups stock, the apricots and mint, and mix well. Soak for 10 minutes or until the couscous has absorbed all the stock.
Preheat the oven to 200 degrees C. Place the turkey on a rack in a medium-sized roasting pan and pour over 150ml hot water.
Using a spoon stuff some couscous into the neck end of the turkey, mounding it a little. Secure the skin flap underneath the bird with the wing tips. Spoon 2 tablespoons lemon juice over. Cover the turkey loosely with oiled foil and roast for 1 3/4 hours. Baste with the juices occasionally, and remove the foil for the last 30 minutes of cooking to brown the skin. The turkey is cooked when the juices run clear.
Meanwhile, fill the lemon halves with couscous. Spread the rest of the couscous in a small ovenproof dish and sit the filled lemon halves on top. Cover with foil and place in the oven for the last 20 minutes of the turkey's roasting time. When the turkey is cooked, remove it from the pan and let it rest on a board for 10 minutes. Skim the fat from the surface of the juices in the pan, then add the sherry and the remaining stock. Bring to the boil on the stove, scraping up the browned bits. Boil for 5 minutes. Season with pepper.
Carve the turkey and serve with the couscous-filled lemons, the extra couscous and the pan sauce. Garnish with mint.