Cook the sushi rice according to package instructions until fluffy and tender. Once cooked, let it cool slightly before mixing in a combination of rice vinegar and sugar that you've heated in the microwave until dissolved.
In a separate bowl, combine your cubed salmon with light soy sauce, Kewpie mayo, sriracha, and sesame oil. Mix everything together until well combined and set aside while you work on preparing your nori sheets.
Cut your nori sheets into squares large enough to fit into muffin tin slots, then lightly grease these slots with cooking spray for easy removal later on. Place a spoonful of sushi rice in each nori square and press it down gently before topping it off with your prepared salmon mixture.
Preheat your oven to 400℉ and bake your filled nori cups for approximately 15 minutes or until they are golden brown on top and the salmon is fully cooked through.
After baking, allow your sushi cups to cool for a few minutes before drizzling extra sriracha or spicy mayo over them. Top with furikake and chopped green onions for added flavor before serving immediately!