Mix rice vinegar, sugar, and salt; fold into the cooked sushi rice and let cool to room temperature
Combine tuna, mayonnaise, sriracha, soy sauce, and sesame oil in a bowl
Place a sheet of nori on a flat surface
Spread a layer of rice on the nori, leaving a border and sprinkle sesame seeds
Add a quarter of the tuna mix in the center, cucumber, avocado, spicy mayo, scallions, and microgreens
Fold nori corners over the center to form a square
Cut into triangles and serve with soy sauce, wasabi, or ginger if desired
