Preheat the oven to 180°C (350°F).
In a small bowl, mix the olive oil, minced garlic, chopped rosemary, salt, and pepper.
Rub the mixture all over the leg of lamb, ensuring it's evenly coated.
Place the lamb in a roasting pan and put it in the preheated oven.
Roast the lamb for about 1.5 hours or until the internal temperature reaches 60°C (140°F) for medium-rare.
Remove from the oven, cover with foil, and let it rest for 15 minutes before carving.