Rinse the sushi rice under cold water until the water runs clear. Combine with water in a saucepan, bring to a boil, then simmer for 20 minutes. Let it rest for 10 minutes after cooking.
Flake the cooked salmon into a bowl, add mayonnaise and sriracha, and mix until well combined.
Mix rice vinegar, sugar, and salt in a bowl until dissolved. Fold into the cooked sushi rice. Spread the rice in a greased baking dish and layer the salmon mixture on top.
Preheat oven to 400°F. Bake for 15-20 minutes until golden and bubbly. Let cool slightly before serving, then top with cucumber, avocado, green onions, nori, and sesame seeds.