Preheat oven to 400°F. Place salmon on a foil-lined baking sheet, drizzle with sesame oil, season with salt and pepper, and bake for 12-15 minutes until cooked through. Let cool, then flake into small pieces, removing any bones or skin.
Rinse sushi rice 3-4 times in cold water until water runs clear. Cook in a rice cooker or on the stovetop with 2¼ cups water. Meanwhile, combine rice vinegar, sugar, and salt in a small saucepan over low heat until dissolved. Transfer cooked rice to a large shallow bowl, pour vinegar mixture over, and fold gently while fanning to cool.
In a medium bowl, combine flaked salmon with softened cream cheese, Kewpie mayo, sriracha, soy sauce, sesame oil, and half the green onions. Mix thoroughly until creamy and cohesive, then taste and adjust seasoning as needed.
Grease a 9x13 inch baking dish. Press the seasoned sushi rice into an even layer across the bottom. Sprinkle furikake generously over the rice, then spread the creamy salmon mixture on top in an even layer.
Reduce oven temperature to 375°F. Bake for 20 minutes until heated through. Switch to broil on high and broil for 3-5 minutes until the top is golden and bubbling, watching closely to prevent burning.
Let cool for 5 minutes. Drizzle with extra Kewpie mayo and sriracha in a zigzag pattern, scatter with remaining green onions and sliced avocado. Serve immediately with roasted seaweed sheets for scooping.