1. Preheat oven to 425 degrees F. Spray a large roasting pan with vegetable cooking spray. Set aside.
2. In a small mixing bowl, whisk together paprika, sugar, cumin, cinnamon, ginger, turmeric, cayenne, mustard, and citrus pepper rub until evenly blended. Set aside 2 Tbsp. of the spice mixture and mix the remaining with 2 Tbsp. of the vinaigrette to make a paste. Rub the paste all over the lamb roast. Set the lamb in the middle of the roasting pan.
3. Add carrots, cauliflower, celery, and onion to a large mixing bowl, drizzle oil and remaining 2 Tbsp. vinaigrette over the vegetables, and toss well to coat. Sprinkle reserved spice mixture over the vegetables and toss well to coat. Place the vegetables in the pan around the roast.
4. Place the pan in the oven. Cook for 15 minutes at 425 degrees F, then reduce heat to350 degrees F. Roast lamb for 1 hour 40 minutes for medium doneness (150 degrees F internal temperature on an instant-read thermometer; rare is 135 degrees F and well done is 170 degrees F).
5. Remove lamb from oven and tent with foil. Transfer vegetables to a large serving bowl, add tomatoes and cilantro, and toss well until evenly mixed. Allow lamb to rest for 10 minutes before carving.
6. Thinly slice lamb and place it on a serving platter with couscous, if desired. Serve warm, with the bowl of vegetables on the side.
Source: Fresh Magazine March, April 2010