Step 1

Bring 2 cups short-grain white sushi rice, rinsed until water runs almost clear, and 2½ cups water to a boil in a medium saucepan, stirring occasionally. Reduce heat to low, cover pan, and cook until water is absorbed, 12–14 minutes. Remove from heat and let sit (still covered) 15 minutes. Gently fluff rice with a fork. Let sit until cool enough to handle but still warm.

Step 2

Meanwhile, using a fork, mix 6 scallions, dark green and pale green parts only, thinly sliced, finely grated zest of 1 large lemon, two 5-oz. cans oil-packed tuna, drained, ½ cup mayonnaise, 1 Tbsp. plus 2 tsp. sriracha, 2 tsp. soy sauce, preferably low-sodium, and 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt in a small bowl until well combined. Taste and season with more salt if needed.

Step 3

Set up a workstation with a small bowl of water, a small bowl of kosher salt, cooked rice (still in pan), tuna filling, and eight 6" squares of plastic wrap.

Step 4

To make 1 onigiri, line an 8-oz. ramekin or bowl with a square of plastic wrap. Dip your hands in water to moisten, then rub with a little salt. (This prevents the rice from sticking to your hands and also flavors the onigiri.) Scoop ½ cup rice into your nondominant hand (keep remaining rice covered) and shape into a ball. Transfer rice ball to prepared ramekin and press onto bottom and up sides, making a well in the center. Fill with 3 Tbsp. tuna filling. Using plastic wrap as a guide, bring rice up and over filling to enclose; squeeze tightly to seal. Remove onigiri from ramekin and form into a triangle shape or a ball; transfer to a platter. Repeat with remaining rice and tuna filling, dipping your hands in water and rubbing with salt each time.

Step 5

Just before serving, place ¼ cup furikake on a small plate. Unwrap onigiri and roll in furikake, adding more furikake to plate as needed. Serve immediately.