Start by ensuring that your sashimi-grade tuna is well-chilled. Using a sharp knife, cut the tuna into small, bite-sized cubes.
In a mixing bowl, combine the cubed tuna with the finely chopped green onions. Add the toasted sesame oil, sriracha sauce, and Japanese mayonnaise to the bowl.
Gently fold the ingredients together until the tuna is evenly coated. Taste and adjust the sriracha if desired.
Transfer the Spicy Tuna to a serving dish and sprinkle the toasted white sesame seeds over the top. Serve immediately.
