Make 10 slits throughout the loin of lamb. Stuff each slit with a piece of garlic.

In a mixing bowl, combine the oil, rosemary, and zest. Season with salt and pepper. Mix well. Rub the entire loin of lamb with the rosemary mixture. Wrap the loin tightly in plastic wrap and refrigerate for at least 24 hours. Remove the lamb from the refrigerator and bring to room temperature. Remove the plastic wrap and discard.

Preheat the oven to 400 degrees F.

Place the lamb in a roasting pan and place in the oven. Roast for 15 minutes. Reduce the heat to 350 degrees F and continue to slow-roast for 45 minutes to 1 hour, or until the internal temperature reaches 135 degrees F. Remove from the oven and set the lamb on a carving board, reserving the pan juices. Allow the lamb to sit for about 10 to 15 minutes before serving. The roast will be a perfect medium rare.

Pour off most of the fat from the pan, leaving about 2 tablespoons of the fat and the brown particles. Place the pan on the stove over medium heat, stir in the flour and cook for 1 minute, stirring constantly. Add the stock and bring to a boil. Season with salt and pepper, and cook for 3 to 4 minutes, or until slightly thickened. Slice the lamb into individual slices. Serve with the couscous and the pan sauce. Garnish with parsley

Place couscous in a large bowl. Cover with boiling water. Cover bowl with plastic wrap and let sit for 30 minutes. Remove plastic wrap and fluff with a fork. Add pine nuts, currants, parsley, shallots, lemon zest, lemon juice, and olive oil and mix well. Season with salt and pepper.