Heat the oven to 425° and place a rack in the center.
Zest the three lemons and then cut in half to juice, set the juice aside. Place the lemon zest, garlic, parsley and four tablespoons of oil in a medium bowl and season with salt and pepper. Stir until evenly combined; set aside.
Unroll the lamb, lay it flat on a cutting board and remove any large pieces of connective tissues. Season the lamb with salt and pepper, then spread the lemon-garlic-parsley paste over the seasoned meat. Roll the lamb back up and tie with twine to evenly secure. Season the exterior with some olive oil, salt and pepper, and place the leg in a roasting pan.
Place the lamb leg in the oven and reduce the temperature to 400°. Roast until the internal temperature reads 135°, about 1 to 1½ hours. Once removed from the oven, transfer to a cutting board and allow to rest for a minimum of 20 minutes, up to 30 minutes. Remove the twine and carve for serving.
While lamb is resting, deglaze the roasting pan with the chicken stock. Transfer to a small bowl, skim off any excess fat. Pour defatted juices into a small sauce pot and reduce lightly. Serve jus alongside of the sliced leg of lamb.
Yields 6-8 servings