Preheat your oven to 350°F (175°C).
Rinse sushi rice under cold water until clear.
Combine sushi rice and water in a rice cooker and cook according to manufacturer instructions.
Once cooked, transfer rice to a large bowl and mix with rice vinegar and sugar.
In a separate bowl, mix mayonnaise with sriracha for a spicy topping (optional).
In a baking dish, layer half of the rice evenly on the bottom.
Add a layer of sliced avocado and cucumber over the rice.
Place the salmon on top of the vegetables.
Spread the spicy mayonnaise mixture over the salmon.
Top with the remaining rice and sprinkle with panko breadcrumbs.
Bake in the preheated oven for 20-25 minutes until golden brown.