Preheat your oven to 400°F and lightly grease a standard muffin tin.
In a large bowl, combine the cubed salmon, sea salt, soy sauce, and mayo, ensuring everything is well coated.
Mix the cooked rice with rice vinegar until evenly combined.
Lay out the nori sheets on a countertop and cut them into squares to fit each muffin tin cavity.
Fill each nori square with 2-3 tablespoons of rice, folding them and placing them into the muffin tin.
Top each nori cup with the salmon mixture, about 2 tablespoons per cup.
Bake for 15 minutes or until the salmon is cooked to your liking.
Once done, remove from the oven, add your chosen garnishes, and serve immediately! Enjoy these cups fresh on the same day, or store any leftovers in an airtight container in the fridge for up to two days.