Rinse the rice until the water runs clear, then drain well. Combine the rice, salt, and water in a saucepan and bring to a boil. Stir once, cover, and cook over low heat for 10 minutes. Remove from the heat and let stand, covered, for 12 minutes.
Meanwhile, warm the rice vinegar, sugar, and salt in a small saucepan just until dissolved. Fold into the rice until glossy and lightly sticky. Let cool slightly.
Line a rectangular pan with plastic wrap, pressing it into the corners. Arrange the salmon and tuna in a tight, even layer. Add the rice and press firmly. Top with the avocado and cucumber, pressing gently, then cover with nori.
Combine the tuna, chives, chile, sriracha, and mayonnaise in a bowl and mix until cohesive. Spread evenly over the nori. Chill until firm, then invert onto a serving platter.
Drizzle with teriyaki and spicy mayonnaise, and finish with chives.