Preheat oven to 450°F (232°C).
Pat the leg of lamb dry with paper towels and place it fat-side up on a rack inside a roasting pan.
In a small bowl, combine minced garlic, chopped rosemary, lemon zest, lemon juice, olive oil, salt, and black pepper to create a coarse paste.
Rub the garlic and herb paste evenly over the entire surface of the lamb.
Roast in the preheated oven for 15 minutes to develop a browned crust.
Reduce the oven temperature to 325°F (163°C) and continue roasting for 1 hour to 1 hour 15 minutes, or until a meat thermometer inserted into the thickest part reads 135°F (57°C) for medium-rare.
Remove the lamb from the oven, tent loosely with aluminum foil, and let it rest for 20 minutes before carving.