Preheat the oven to 450° F. Chop up the garlic and herbs in the food processor. When they are well chopped, add the mustard and purée until a smooth paste forms.
Smear the paste over the exterior of the lamb and place on a roasting pan. Season liberally with sea salt and roast for 15 minutes at 450° F. Turn the oven down to 325° F and cook for 30 to 40 minutes more, or until a meat thermometer registers 130 to 140° for rare to medium-rare. Let the roast rest for 15 minutes before carving and serving.