Combine all ingredients for the fresh herb paste in a food processor or high powered blender. Blend until combined and mixture has the consistency of pesto.
Since your leg of lamb is already boneless, it has already been butterflied for you.* Lay it on a work surface with the inside facing up. Spread about ⅔ of the paste on the inside of the roast. Roll the leg up into a roast shape and tie with cotton kitchen twine. Rub the remaining herb paste all over the outside of the roast.
Place on a rack in a roasting pan and roast for 60-90* minutes, until the internal temperature has reached your desired level of doneness (***see chart in notes. I roasted mine to 135°F)
Remove from oven and allow to rest for twenty minutes before carving.
*If you have a bone in leg of lamb, butterfly the roast and remove the bone. It is a bit daunting, so we suggest asking your butcher to do it for you if you are unable to find a boneless roast.**Cooking time varies depending on the size and shape of the roast. After 1 hour use a thermometer to take the internal temperature. If the temperature has not reached your desired doneness, continue to roast and check the temperature every 15-20 minutes until it does. If the outside starts to brown too much, tent with foil. A good rule of thumb is that it takes about 20 minutes per pound for the roast to cook, however always use a meat thermometer to ensure roast is cooked correctly.***The USDA recommends cooking to an internal temperature of 145. If you would prefer to select a different level of doneness, please consult this chart. Temperature Chart: Rare: 115 to 120°F Medium-Rare: 120 to 125°F Medium: 130 to 135°F Medium-Well: 140 to 145°F Well-Done: 150 to 155°F