01 - Preheat oven to 400°F. Pat lamb leg completely dry with paper towels to ensure proper browning.
02 - In small bowl, combine olive oil, chopped rosemary, thyme, lemon zest, salt, and pepper until well blended.
03 - Using sharp knife, make deep slits all over lamb. Insert halved garlic cloves into each slit for maximum flavor infusion.
04 - Rub herb mixture thoroughly over entire surface of lamb, pressing gently to adhere and ensure even coverage.
05 - Arrange onion slices, carrot chunks, and halved garlic bulb in large roasting pan to create aromatic bed for lamb.
06 - Place seasoned leg of lamb on top of vegetable bed. Pour wine or stock into bottom of pan.
07 - Roast at 400°F for 20 minutes to develop golden-brown exterior crust.
08 - Reduce temperature to 350°F. Continue roasting for 1 hour 10 minutes for medium-rare (internal temperature reaches 140°F), basting occasionally with pan juices.
09 - Remove lamb from oven, cover loosely with foil, and let rest 15-20 minutes to allow juices to redistribute throughout meat.
10 - Carve lamb into slices and serve with roasted vegetables and pan juices spooned over top.