Prepare the Bamboo Mat: Wrap your bamboo sushi rolling mat securely in a few layers of plastic wrap. This prevents the rice from sticking in the grooves and makes cleanup completely effortless.

Make the Spicy Tuna Filling: In a medium mixing bowl, combine the finely chopped sushi-grade tuna, Japanese mayonnaise, Sriracha, and toasted sesame oil. Gently fold the mixture together until the tuna is evenly coated in the creamy, spicy sauce. Set aside.

Prepare the Nori: Place one sheet of nori rough-side up on your plastic-wrapped bamboo mat.

Spread the Rice: Lightly wet your hands in a small bowl of water to prevent sticking. Grab about half a cup of the seasoned sushi rice and gently spread it evenly over the nori sheet, leaving a 1-inch border of empty seaweed at the top edge. Do not smash or press the rice down too hard.

Add the Fillings: Spoon half of the spicy tuna mixture in a horizontal line across the lower third of the rice (closest to you). Lay half of the julienned cucumber matchsticks directly alongside the tuna.

Roll the Sushi: Lift the bottom edge of the bamboo mat over the filling, tucking it tightly with your fingers to form a cylinder. Continue to roll forward, applying gentle, even pressure, until you reach the bare strip of nori. Dab a tiny bit of water on the bare edge to help seal the roll, then complete the roll.

Slice: Place the roll on a clean cutting board. Dip the blade of a very sharp knife into water and shake off the excess. Cut the roll directly in half. Then, slice each half into 3 or 4 even pieces. Wipe your knife with a damp towel between every single cut for the cleanest slices.

Garnish and Serve: Repeat the process with the remaining ingredients to make the second roll. Sprinkle the finished rolls with toasted sesame seeds and serve immediately with soy sauce, pickled ginger, and wasabi.