Prep: Preheat the oven to 375F. Use a sharp knife to cut slits in the surface of the lamb.
Mix: In a bowl, mix together garlic, lemon juice, olive oil, rosemary, salt, and pepper.
Marinate: Rub the mixture all over the lamb, ensuring it gets into all the slits.
Roast: Place the lamb in a roasting pan and roast up to 90 minutes or until desired level of doneness is achieved.
Serve: Let the lamb rest for a few minutes before slicing and serving.