Place 2 tablespoons of macadamia nut oil, and the rosemary, thyme, sage, garlic, pepper, and sea salt (if using) in a small food processor. Chop until herbs and garlic are minced to a fine consistency and there are no large pieces.
Rub or brush lamb with the oil mixture.
Wrap lamb in plastic wrap, eliminating as much air as possible. Place on a small tray and refrigerate for at least 2 hours, up to 24 hours.*
When you are ready to cook, preheat oven to 400F degrees. Remove lamb from plastic wrap.
Heat 2 teaspoons of macadamia nut oil in a small roasting pan with oven-safe handles over medium-high heat. Make sure pan is hot before introducing lamb.
Place the lamb in the pan and brown on both sides, about 3-4 minutes on each side.
When lamb is browned, place meaty side up. Brush a thin layer of the mustard over the lamb at this time if desired. Place pan in oven, on middle rack. Roast for 20 minutes for medium rare, 22 to 24 minutes for medium-well, or until meat reaches desired doneness. Remove from oven, place on carving tray and cover with foil for five to ten minutes before serving.