Preheat oven to 375°F (190°C).

Rinse sushi rice under cold running water in a fine-mesh strainer, swishing with your hand until water runs clear. This removes excess starch.

Cook rice according to package instructions in rice cooker or pot, typically using 2.5 cups water for 2 cups rice.

While rice cooks, combine rice vinegar, sugar, and salt in a small bowl. Stir until sugar and salt dissolve completely.

When rice finishes cooking, transfer to large bowl and fluff gently with fork or rice paddle. Drizzle vinegar mixture over hot rice and use cutting motion to fold it in without crushing grains. Let cool slightly until warm but not hot.

Press seasoned rice evenly into bottom of 9x13 inch baking dish, creating layer about 1 inch thick. Use dampened hands or back of spoon to prevent sticking and ensure even coverage.

Pat salmon pieces completely dry with paper towels. In mixing bowl, combine diced salmon with mayonnaise, Sriracha, sesame oil, and half the green onions. Mix gently but thoroughly to coat all salmon pieces. Adjust Sriracha to taste preference.

Spread salmon mixture evenly over rice layer, covering completely. Use spatula to smooth top roughly even for consistent cooking.

Bake in preheated oven for 25-30 minutes, until salmon is cooked through and top is slightly golden around edges. Salmon should flake easily with fork but still look moist.

Remove from oven and let rest for 5 minutes. Garnish generously with furikake seasoning, remaining green onions, nori strips, and tobiko if using.

Serve warm, scooping portions with large spoon. Set out soy sauce, extra Sriracha, and wasabi on the side for customization.