01 - Preheat oven to 300°F. Thoroughly pat the lamb dry with paper towels and place in a large roasting pan.
02 - In a small bowl, whisk together garlic, lemon zest, lemon juice, oregano, olive oil, salt, and pepper until well combined.
03 - Rub the marinade thoroughly over the entire surface of the lamb. Make shallow incisions in the meat and massage the 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 pan around the vegetables and meat.
06 - Cover the roasting pan tightly with aluminum foil. Roast for 2.5 hours.
07 - Remove foil and increase oven temperature to 400°F. Roast uncovered for 30 minutes until the lamb develops a golden, caramelized exterior and reaches desired tenderness.
08 - Transfer lamb to a cutting board and let rest, loosely covered with foil, for 15 minutes before carving. Serve with roasted vegetables and pan juices.