01 - Preheat oven to 300°F. Pat the lamb thoroughly dry with paper towels and place in a large roasting pan.
02 - In a small bowl, combine garlic, lemon zest and juice, oregano, olive oil, salt, and black pepper. Mix thoroughly to form a paste.
03 - Rub the marinade generously over all surfaces of the lamb. Using a sharp knife, make shallow incisions in the meat and massage marinade into these cuts for deeper flavor penetration.
04 - Place potatoes, onions, and carrots around the lamb in the roasting pan, distributing them evenly.
05 - Pour broth and wine (if using) into the bottom of the pan around the vegetables and meat.
06 - Cover the pan tightly with aluminum foil. Roast for 2.5 hours to allow the meat to become tender and flavorful.
07 - Remove foil and increase oven temperature to 400°F. Continue roasting uncovered for 30 minutes, or until the lamb develops a golden-brown crust and reaches desired doneness.
08 - Let the lamb rest, loosely covered with foil, for 15 minutes before carving. This allows juices to redistribute throughout the meat. Serve with roasted vegetables and pan juices.