Wash rice thoroughly and cook
Make a very small bowl of salt and sesame seeds
Mince the tuna with a knife and in a medium bowl, mix the tuna with the soy sauce, sesame oil, and sliced green onions
Use a paddle to cut the rice and let in a lot of air so it fluffs it up. Let cool slightly so you can handle the rice
Make a ball of rice (about 1/3 or 1/2 cup), make a hole in the middle, add in a large spoonful of filling. Top with a bit more rice to close the ball.
With damp hands, dip a finger into the sesame salt mix and rub into your palms.
Take the ball and press the rice ball into shape. (try doing this as few times as possible, the tighter you press the rice ball, the harder the rice ball will be.
Make your hands into a triangle shape and press the sides into form, rotate each time.
* Optionally, you can use a mold to do this!
Lay half piece of nori down on your work surface. Stand the onigiri in the middle, lay it down and fold the nori over. Tuck in the edges, and roll to it's side so an open segment is on top.
Add a bit more of your filling on the top, serve and enjoy! These are best when they are fresh and warm.
Depending on the size you make each rice ball, you will be able to make more or less onigiri with your ingredients.