Pat the beef dry with paper towels. Season all sides evenly with salt and black pepper.
Heat the oil in a skillet over high heat. Once hot, sear the beef for 30 to 45 seconds per side. You want a browned exterior while keeping the inside rare. Transfer to a plate and let it cool slightly.
In a shallow bowl, stir together the soy sauce, rice vinegar, sesame oil, ginger, and garlic.
Place the seared beef into the sauce and refrigerate for 15 minutes, turning occasionally.
Remove the beef from the marinade. Slice it thinly against the grain and arrange on a serving plate. Garnish with green onions and sesame seeds, and drizzle a little extra sauce on top.
