01 - Preheat the oven to 400°F. Pat the lamb leg dry with paper towels.
02 - In a small bowl, mix olive oil, chopped rosemary, thyme, lemon zest, salt, and pepper.
03 - Using a sharp knife, make deep slits all over the lamb. Insert halved garlic cloves into the slits.
04 - Rub the herb mixture thoroughly over the lamb, ensuring even coverage.
05 - Arrange the onion slices, carrot chunks, and halved garlic bulb in a large roasting pan to make a bed for the lamb.
06 - Place the lamb leg on top of the vegetables. Pour wine or stock into the pan.
07 - Roast for 20 minutes, then reduce oven temperature to 350°F.
08 - Continue roasting for 1 hour 10 minutes for medium-rare (internal temp 140°F), basting occasionally with pan juices.
09 - Remove lamb from oven, loosely cover with foil, and let rest for 15-20 minutes before carving.
10 - Serve slices of lamb with roasted vegetables and pan juices.