Dice the sushi-grade salmon into small, uniform cubes and place them in a chilled mixing bowl.
In a separate small bowl, whisk together the mayonnaise, sriracha, toasted sesame oil, and coconut aminos until the dressing is smooth and fully emulsified.
Gently fold the salmon cubes into the spicy dressing until every piece is evenly coated.
Julienne the cucumber into thin matchsticks and thinly slice the avocado into long strips.
Season the cooked white rice with the rice vinegar and half of the black sesame seeds, fluffing gently with a fork to combine.
Lay a sheet of nori on a clean, dry surface and spread half of the seasoned rice over the left third of the sheet.
Arrange half of the spicy salmon, cucumber matchsticks, and avocado slices diagonally across the rice-covered section.
Fold the bottom left corner of the nori over the fillings and continue rolling to form a cone shape, using a tiny drop of water on the far edge to seal.
Repeat the process for the second hand roll, sprinkle with the remaining sesame seeds, and serve immediately while the nori is crisp.