Thoroughly rinse the sushi rice under cold water until it runs clear. Cook according to package directions.

Transfer the cooked rice to a bowl and gently mix in rice vinegar, sugar, and salt while still warm.

In a mixing bowl, flake the drained tuna and mix in mayonnaise, sriracha, sesame oil, soy sauce, and chopped green onion.

Wet your hands with salted water and form a handful of the seasoned rice into a ball. Create a well, fill with the tuna mixture, and encase with more rice, shaping into a triangle.

Wrap each formed onigiri with a strip of nori. Repeat the process with remaining rice and filling.

Serve immediately or store by wrapping each onigiri in plastic wrap and refrigerating up to two days.