Preheat the oven to 375°F (190°C). Lightly grease a baking dish and set it aside.
Place the warm cooked rice in a bowl. Add the rice vinegar, sugar, and salt, then gently mix until evenly seasoned.
Spread the seasoned rice into the prepared baking dish. Press it down lightly into an even layer without compacting it too much.
In a separate bowl, combine the cooked salmon, mayonnaise, sriracha, soy sauce, sesame oil, and cream cheese if using. Mix gently until creamy but still chunky.
Spoon the spicy salmon mixture evenly over the rice layer. Smooth the top lightly.
Sprinkle furikake seasoning evenly over the top of the salmon mixture.
Bake uncovered for 20–25 minutes, until the edges are bubbling and the top is lightly golden.
Optional: Turn on the broiler for 1–2 minutes to lightly crisp the top. Watch closely to prevent burning.
Remove from the oven and let rest for 5 minutes. Top with green onions, sesame seeds, and diced avocado if desired.
Serve warm and scoop with roasted seaweed sheets or enjoy with a spoon.