Rinse the sushi rice under cold water in a fine-mesh sieve until the water runs clear. In a medium pot, combine the rinsed rice with water, then bring to a boil. Reduce heat and cover the pot, allowing the rice to simmer gently for 18-20 minutes until tender.

Prepare the vinegar mixture by whisking together rice vinegar, sugar, and salt in a small bowl until dissolved. When the rice finishes cooking, remove from heat, let stand covered for 10 minutes, fluff with a fork, and fold in the vinegar mixture.

In a separate mixing bowl, combine diced salmon fillet, mayonnaise, sriracha sauce, sesame oil, and chopped green onions. Mix until well incorporated.

Spread the sushi rice evenly in a greased 9x13-inch baking dish. Layer the salmon mixture on top, spreading it out to cover the rice.

Preheat your oven to 375°F (190°C). Bake the assembled sushi bake for 25-30 minutes until the top is golden brown and bubbly.

Let the dish cool for about 5 minutes, then garnish with sliced green onions, nori strips, and optional tobiko. Serve warm.