In a small bowl, combine flaked salmon with mayonnaise, soy sauce, and wasabi if using. Mix gently with a fork until well combined but not mushy, keeping some texture visible in the salmon. Set aside.

Place a small bowl of water nearby and dampen a clean kitchen towel with it. Lay out a small plate or cutting board where you'll shape your onigiri, and arrange your nori strips within arm's reach.

Dip your hands into the water bowl and keep them lightly damp throughout the process to prevent rice from sticking. Rewet hands as needed.

Scoop roughly 1/3 cup of cooled rice into your damp palm and gently form it into a loose ball. Ensure rice is at room temperature or cooler.

Using your thumb, push a small indent into the center of the rice ball about the size of your thumbnail, deep enough to hold about one tablespoon of salmon filling.

Spoon one tablespoon of the prepared salmon mixture into the indent. Do not overfill.

Gently fold the rice around the filling by cupping your hand and rotating the ball, folding rice inward to completely cover the filling.

Press the sealed rice ball gently into a triangle shape using your three middle fingers to create three flat sides, applying even pressure without squeezing too hard.

Wrap one nori strip around the middle or bottom of the rice triangle where your fingers grip it, ensuring it is snug but not tearing.

If desired, sprinkle toasted sesame seeds or furikake on top for extra flavor and visual appeal.

Arrange completed onigiri on a plate and serve immediately or wrap individually in plastic wrap for portable lunches. Best eaten within a few hours.