Rinse the sushi rice under cold water until the water runs nearly clear. Combine with 2.5 cups of water in a medium saucepan and bring to a boil. Reduce heat to low, cover, and simmer for about 15 minutes. Remove from heat and let rest, covered, for at least 10 minutes.

While the rice is resting, mix rice vinegar, sugar, and salt in a small bowl until dissolved. Fluff the rice with a fork and fold in the vinegar mixture.

Spread the seasoned sushi rice evenly across the bottom of a 9x13 baking dish and press down gently to create a flat layer. Allow it to cool slightly.

In a mixing bowl, combine diced fresh salmon with mayonnaise, sriracha, sesame oil, and green onions. Stir until well blended.

Spread the salmon mixture evenly over the rice. Preheat oven to 375°F (190°C) and bake for 25 to 30 minutes until golden brown and bubbly.

Remove from oven, let cool for a few minutes, and garnish with sliced green onions, nori strips, and optional tobiko.