Prepare the Marinade: In a medium mixing bowl, whisk together the soy sauce, sesame oil, grated ginger, minced garlic, and wasabi paste (if desired) until smooth and well combined.
Marinate the Tuna: Carefully add the cubed Ahi tuna to the marinade, ensuring each piece is coated evenly. Allow the tuna to marinate at room temperature for at least 15 minutes.
Coat with Sesame Seeds: Once marinated, remove the tuna cubes from the marinade and set them aside. Pour the sesame seeds onto a small plate. Roll each tuna cube gently in the sesame seeds, pressing lightly to adhere the seeds to all sides.
Heat the Pan: In a large skillet or frying pan, heat the vegetable oil over medium-high heat until it becomes shimmering and hot.
Sear the Tuna: Place the sesame-coated tuna cubes in the hot skillet. Sear each side for approximately 30-45 seconds, allowing them to develop a golden crust while keeping the center rare.
Serve: Arrange the sesame-crusted Ahi tuna bites on a decorative serving platter. Garnish with thinly sliced green onions.
Notes
Serve with small dipping bowls of soy sauce and consider pairing with pickled ginger and wasabi.