In a bowl or measuring cup, whisk together the olive oil, lemon juice, salt, pepper, mint leaves, and rosemary. Add the marinade to a large ziplock bag or casserole dish. Add the leg of lamb and turn it to make sure the marinade is evenly distributed. Marinate in the refrigerator for at least 2 hours or overnight.

Remove the lamb from the refrigerator and allow it to come to room temperature while the grill preheats to medium high. Skewer the meat lengthwise (I used four long metal skewers) to help it stay together on the grill. Place the meat on the preheated grill, brush with additional marinade and cook until internal temperature reaches desired doneness (Rare: 125 degrees; Medium rare: 135 degrees; Medium: 145 degrees) I recommend medium rare for lamb, which will take 8-12 minutes per side.

When the lamb is at the correct temperature, remove it to a cutting board and tent with foil for 10 minutes before slicing.

While the lamb grills, whip up the sauce. In a bowl, whisk together the sugar, hot water, salt, and black pepper until the sugar is dissolved. Stir in the mint and vinegars until well combined. To serve, slice the lamb into thin strips across the grain then spoon over mint sauce. Serve warm.