If you don't want to turn on the oven, you can grill the lambs butterflied flat.
Preheat the oven to 350 degrees. Combine the bread crumbs, herbs, pistachios, garlic, chili flakes, lemon zest, salt, zest, pepper in a bowl and add the oil. You can also put all these ingredients in a food processor and pulse a few times. Place lamb on a sheet pan. Spoon the Dijon mustard over the lamb to cover then pat the crust over the mustard. The lamb will benefit from an overnight marinade if you have the time, however even 3-4 hours would be great too.
Roast lamb for 1 to 1 1/2 hours or until desired doneness. Check temperature in the thickest part of the roast - 125 degrees is medium rare.
When the lamb is ready, remove from oven and let rest 15-20 minutes under a tent of foil. Place on cutting board and slice against the grain. Place on serving platter and garnish with fresh herb bundles. Pour the pan drippings in a bowl and serve over meat as well if desired. Serves 8.