In a mixing bowl, combine the extra virgin olive oil, lemon zest, lemon juice, minced garlic, minced rosemary, kosher salt, and black pepper. Whisk together until well combined.
Place the boneless leg of lamb in a large resealable bag or a shallow dish. Pour the marinade over the lamb, ensuring it’s well-coated on all sides. Seal the bag or cover the dish with plastic wrap and refrigerate for at least 4 hours, or preferably overnight.
About 30 minutes before you’re ready to grill, preheat your grill to medium-high heat.
Remove the lamb from the marinade and let any excess marinade drip off. Place the lamb on the grill. Grill for about 15-20 minutes on each side, or until the internal temperature reaches your desired doneness (135°F for medium-rare).
Once the lamb is cooked to your liking, remove it from the grill and let it rest for at least 10 minutes. After resting, slice the lamb against the grain and serve.