Step 1 Rinse the preserved lemons well under cold water. Remove the inside pulp and discard.
Step 2 Using a mortar and pestle, or in a small bowl with a sturdy spoon, grind the garlic cloves to a paste with one-fourth teaspoon salt. Place the garlic paste, preserved lemons, lemon juice, cilantro, cumin, paprika and 2 tablespoons olive oil in a food processor or large mortar and puree until smooth.
Step 3Smear the marinade all over the chicken and season lightly with pepper. (You will not need salt as the preserved lemons are already very salty.) Stuff the squeezed lemon half into the body cavity. Transfer the chicken to a dish and leave it to marinate in the fridge for about 6 hours, or overnight if you prefer.
Step 4When you are ready to roast the chicken, heat the oven to 350 degrees.
Step 5Oil a roasting pan with the remaining tablespoon oil. Place the chicken in the pan and roast until done, about 1 hour and 15 minutes, basting every 15 minutes or so with the juices in the pan. After about 1 hour, pierce the leg with a skewer or sharp knife; the chicken is ready if the juices run clear and will need a little more time if the juices are still pink. Or place a thermometer into the thigh, avoiding the bone; the chicken is done when the temperature reaches 165 degrees. Transfer the chicken to a board to relax for 10 minutes, loosely covered with foil.
Step 6To make some gravy, pour off most of the oil from the pan and place the pan on the stove over medium heat. Add the water and bring to a gentle simmer. Drain any juices from the chicken into the pan, and scrape the pan for any caramelized bits to season the gravy. Taste the gravy, and add a little water if desired to thin.