01 - In a small bowl, combine soy sauce, rice vinegar, sesame oil, grated ginger, and minced garlic. Reserve half of the mixture for serving as a dipping sauce.
02 - Pat tuna steaks dry with paper towels. Brush all sides with the remaining marinade.
03 - On a shallow plate, mix together white sesame seeds, black sesame seeds, sea salt, and black pepper. Press each tuna steak into the seed mixture, ensuring all sides are evenly coated.
04 - Heat neutral oil in a heavy skillet over high heat. When the oil is hot and shimmering, carefully add the coated tuna steaks.
05 - Sear the tuna for 45 to 60 seconds per side for rare, or up to 2 minutes per side for medium-rare, allowing the crust to brown while keeping the interior pink.
06 - Transfer the seared tuna to a cutting board. Let rest for 2 minutes, then slice into 1/2-inch thick pieces.
07 - Arrange sliced tuna on serving plates. Drizzle with reserved sauce and garnish with sliced scallions and lime wedges if desired.