Preheat the oven to 325°F (163°C).

In a bowl, combine garlic, rosemary, thyme, olive oil, salt, pepper, and lemon juice to create the marinade.

Rub the marinade all over the leg of lamb, ensuring it is well coated. Let it marinate for at least 30 minutes at room temperature or up to overnight in the refrigerator.

Place the marinated leg of lamb in a roasting pan, bone side down.

Roast in the preheated oven for about 1.5 to 2 hours, or until the internal temperature reaches 135°F (57°C) for medium-rare.

Baste the lamb with its juices every 30 minutes to keep it moist.

Once cooked, remove the lamb from the oven and let it rest for 15-20 minutes before carving.