In a medium bowl, whisk together the tamari, peanut oil, mirin, sesame oil, garlic, and ginger. Add the meat and turn to coat. Cover and marinate in the refrigerator for 4 to 6 hours. Prepare a medium-high gas or charcoal grill fire. Remove the meat from the marinade and pat dry. Grill, turning every 2 minutes, until cooked to your liking, 6 to 8 minutes for medium . Transfer to a cutting board, cover loosely with foil, and let rest for 5 to 10 minutes. Thinly slice across the grain and serve sprinkled with the scallions and sesame seeds.
