Preheat your oven to 400°F (200°C) and lightly grease an 8x8-inch baking dish.
Combine the cooked sushi rice with rice vinegar, sugar, and salt. Press this mixture into the bottom of your prepared baking dish.
Mix together the flaked salmon, mayonnaise, Sriracha sauce, soy sauce, and sesame oil until well combined. Spread this mixture evenly over the rice layer.
Sprinkle shredded mozzarella cheese over the top and bake for about 18–20 minutes or until the cheese is melted and bubbly.
Remove from the oven, let it cool slightly, and garnish with sliced green onions and toasted sesame seeds before serving.