Rinse sushi rice under cold water until the water runs clear. In a pot, combine rinsed rice and water. Bring to a boil, then cover and reduce heat to low. Cook for 20 minutes and remove from heat. Let it sit, covered, for an additional 10 minutes.
In a small bowl, mix the rice vinegar, sugar, and salt until dissolved. Once the rice has rested, fluff it with a fork and gently fold in the vinegar mixture. Set aside.
In a bowl, combine the flaked salmon, mayonnaise, and sriracha. Mix until well combined.
In a baking dish, spread half of the seasoned sushi rice evenly on the bottom. Top with the salmon mixture, spreading it out gently. Follow with the remaining rice on top, smoothing it out.
Place the baking dish in the preheated oven and bake for about 15 minutes, or until heated through and slightly golden on top.
Remove from the oven and let cool for a few minutes. Top with sliced avocado, chopped green onions, and sprinkle sesame seeds over the top for an added crunch.
Use the strips of nori to scoop out portions of the sushi bake, or serve it on its own.