Prepare Sushi Rice: Rinse the sushi rice under cold water until the water runs clear. In a rice cooker, combine the rice and water, then cook according to the manufacturer's instructions. Once cooked, let it sit for 10 minutes.
Season Rice: In a small bowl, mix rice vinegar, sugar, and salt until dissolved. Gently stir this mixture into the cooked sushi rice while it's still warm. Set aside to cool.
Make Spicy Salmon Mixture: In a large bowl, combine the diced salmon, sriracha, mayonnaise, and soy sauce. Mix well to ensure the salmon is evenly coated.
Layer the Bake: Preheat your oven to 375°F (190°C). In a baking dish, spread the seasoned sushi rice evenly on the bottom. Top with the spicy salmon mixture, spreading it out evenly over the rice.
Bake: Bake in the preheated oven for 15-20 minutes, or until the salmon is cooked through and the top is slightly golden.
Garnish and Serve: Remove the baking dish from the oven and let it cool slightly. Top with sliced avocado, cucumber, chopped green onions, and sprinkle with sesame seeds.
Serve with Nori: Cut into squares and serve warm with nori sheets for wrapping each bite.