First, marinate the lamb. In a non-reactive container large enough to hold all the lamb racks side by side, combine the juice, soy sauce, and honey. Stir in the scallions, red pepper flakes, and garlic. Add the lamb racks, bone side up, cover with plastic wrap, and refrigerate overnight. You can also transfer the marinade to a re-sealable plastic bag and marinate the lamb racks in the bag, turning them from time to time.