To make the marinade: In a medium bowl, combine wine, orange juice, soy sauce, garlic, mint, and gingerroot. In a small bowl, mix wasabi powder with ¼ cup marinade mixture. Stir the wasabi mixture into the marinade.
Place lamb racks in a large zip-top plastic bag and pour in the marinade over the lamb (or divide lamb and marinade evenly into several bags). Seal tightly and refrigerate at least 8 hours or overnight, turning the bag several times.
Preheat oven to 500 degrees. Place a metal rack in a shallow roasting pan and spray rack and pan with cooking spray. Remove lamb racks from marinade, reserving marinade. Pour marinade into a microwave-safe bowl; microwave 1 minute.
Place lamb racks, top side up, on the roasting rack. Roast 20 minutes, basting with marinade several times. Remove lamb from oven. Reduce heat to 350 degrees. Sprinkle 3 tablespoons bread crumbs over top of each rack. Drizzle ½ tablespoon melted butter over bread crumbs, then drizzle about 1 tablespoon reserved marinade over top of each rack. Return the lamb racks to the oven 15 to 20 minutes, or until an instant-read thermometer registers 135 degree (medium-rare).
Remove racks from oven and tent with aluminum foil; let rest 5 minutes. Carve chops between the bones, then serve on individual dinner plates atop a nest of Arugula and Watercress Salad.