Cook sushi rice according to package instructions.
In a microwave-safe bowl, combine rice vinegar and sugar. Microwave for about 30 seconds, or until the sugar dissolved. Pour the vinegar mixture over the cooked rice and mix until well combine. Set aside while you prepare the salmon mixture.
Preheat the oven to 400℉.
In a bowl, combined diced or cubed salmon, soy sauce, Kewpie mayo, sriracha, and sesame oil. Mix until well combined. Set aside.
Cut the nori sheets into 4 rectangles or squares, large enough to fit into the muffin tins.
Assemble the Sushi Cups: Lightly grease the muffin tin with cooking spray. Add a spoonful of sushi rice onto the center of each nori square, then press it down lightly into each muffin tin insert. Repeat until the muffin tin is full. Then add a layer of salmon mixture on top of the rice.
Bake in the oven at at 400℉ for 15 minutes, or until the salmon is cooked through and the tops are slightly golden brown.
Remove the sushi cups from the oven and let them cool for a few minutes. Drizzle some more sriracha or spicy mayo on top. Garnish with furikake and chopped green onions. Serve immediately and enjoy!