Rinse the sushi rice until the water runs clear. Cook it according to package directions, typically with 2 1/4 cups of water. Once cooked, transfer the hot rice to a large mixing bowl.

In a small saucepan, combine the rice vinegar, sugar, and salt. Heat gently, stirring until the sugar and salt are completely dissolved. Do not boil.

Pour the vinegar mixture evenly over the hot rice. Using a spatula, fold the mixture into the rice gently, taking care not to mash the grains. The goal is glossy, well-separated, slightly sticky grains. Set aside and allow the rice to cool slightly while you prepare the filling.

Preheat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.

If your salmon fillets aren't already cooked, bake or air-fry them until just cooked through and easily flaked. Gently flake the salmon into medium-sized pieces. We want texture, not mush. Transfer the salmon to a large bowl.

Add the softened cream cheese, kewpie mayo, sriracha, soy sauce, sesame oil, and sliced green onions to the flaked salmon. Mix everything together thoroughly until the filling is uniformly creamy and pink. Taste and adjust the spice level with more sriracha, if desired.

Press the prepared seasoned sushi rice evenly into the bottom of the prepared 9x13-inch baking dish. This layer should be compact and even. Sprinkle the rice layer evenly with half of the furikake seasoning.

Gently spread the entire spicy salmon filling mixture over the rice layer. Try not to press down too hard, maintaining a fluffy texture. Smooth the topping with a spatula.

Sprinkle the remaining furikake seasoning over the top. Bake the baked sushi casserole in the preheated oven for 15-20 minutes, or until the topping is lightly golden brown and bubbling along the edges.

Remove from the oven. Drizzle generously with unagi sauce and extra sriracha or spicy mayo, if using. Serve immediately while warm, alongside chopped avocado slices and quartered nori sheets.