01 - Preheat the oven to 320°F.
02 - Pat the lamb shoulder dry and score the fatty side with a sharp knife in a diamond pattern. Rub all over with olive oil, salt, and pepper.
03 - In a small bowl, combine minced garlic, rosemary, thyme, oregano, lemon zest, and lemon juice. Mix thoroughly to form a cohesive paste.
04 - Massage the herb paste into the lamb, working it deeply into the scored cuts for maximum flavor penetration.
05 - Arrange the sliced onions, carrot chunks, and celery pieces evenly across the bottom of a large roasting pan to create a vegetable bed.
06 - Place the seasoned lamb shoulder on top of the vegetables, fatty side facing upward.
07 - Pour the wine or chicken broth around the base of the lamb, avoiding direct pouring over the meat. Cover the roasting pan tightly with aluminum foil.
08 - Roast covered for 2.5 hours at 320°F until the meat begins to tenderize.
09 - Remove the foil and increase oven temperature to 400°F. Roast uncovered for an additional 30 minutes until the surface develops a golden-brown crust and the meat is fork-tender.
10 - Transfer the lamb to a cutting board and let rest, loosely covered with foil, for 15 minutes to allow juices to redistribute. Carve and serve with roasted vegetables and pan juices.