In a large bowl, add the mayo or yogurt, sriracha, vinegar, soy sauce, and sesame oil and mix to thoroughly combine. Stir in the salmon and scallions until combined, breaking up the salmon until a more uniform smooth texture forms.
Stack your nori sheets on top of each other and use scissors to cut halfway to the center (see video for how to assemble and cut!). Now we have four quadrants to add our four layers.
Add a scoop of salmon (about ¼ cup) to one quadrant and spread it out evenly. Top with another drizzle of sriracha, if you’d like. Add avocado slices to the next quadrant, arranging them into one layer. Add cucumber slices to the next quadrant. Add your cooked rice (about ¼ cup, make sure it’s warm so it sticks better) to the last quadrant, using your fingers to gently spread/press it out into an even layer (wet your fingers to prevent rice from sticking to them).
Now carefully fold each quadrant on top of the other into a square, starting with the rice quadrant (see video)
Serve as is or with some soy sauce for dipping, if you’d like.