Trim excess fat from lamb. Cut several 1/2-inch-wide slits randomly into top and sides of roast. Insert garlic slivers into slits. In a small bowl stir together coriander seed, lemon peel, olive oil, cumin seed, salt, and pepper. Rub lamb surface with spice mixture. Cover and chill for several hours or overnight, if desired.
Preheat oven to 350 degree F. Place lamb on a rack in a shallow roasting pan. Roast lamb for 1-3/4 to 2-1/4 hours or until a meat thermometer inserted in the thickest portion of the meat registers 140 degree F for medium-rare doneness. or 155 degree F for medium doneness. If desired, add assorted cut up vegetables during last 45 minutes of cooking.
Remove lamb from oven. Loosely cover with foil. Let stand for 10 minutes (the temperature of the meat will rise about 5 degree F during standing time). Slice and serve lamb with the roasted vegetables, if desired. Makes 10 servings.