Preheat your oven to 400°F (200°C). Grease an 8x8-inch baking dish with cooking spray or butter.

In a bowl, gently fold the cooked sushi rice (slightly warm or at room temperature) with seasoned rice vinegar until each grain is lightly coated. Spread the rice evenly across the bottom of your baking dish, pressing down gently with a spatula to create a compact, even layer about ¾-inch thick. Sprinkle with half the furikake.

In another bowl, combine the flaked salmon (skin and bones removed), mayonnaise, sriracha, soy sauce, softened cream cheese, sesame oil, and green onions. Mix with a fork until the mixture becomes creamy and smooth with a thick, spreadable consistency. Taste and adjust sriracha for heat preference.

Dollop the spicy salmon mixture over the rice layer, then spread it evenly to all edges with a spatula, creating a uniform layer about ½-inch thick. Sprinkle the remaining furikake and mozzarella cheese over the top in an even layer.

Bake for 15-18 minutes, watching for the top to become bubbly with light golden-brown spots forming around the edges and on the cheese. You'll know it's ready when you see small bubbles breaking through the surface. Avoid overbaking to prevent the salmon from drying out.

Remove from oven using oven mitts and let rest for 5 minutes. This cooling time lets the layers set properly. Top with extra sliced green onions, avocado slices, and cucumber pieces if desired. Cut nori sheets into 2-inch squares with kitchen scissors and serve on the side for scooping.