Using a sharp knife, cut the tuna into about 1/2 inch cubes. Combine shoyu, rice vinegar, sesame oil, hoisin, scallions, and the white and black sesame seeds in a mixing bowl. Stir in the tuna, cover and let marinade for an 1-2 hours or, ideally, overnight.
Cook quinoa based on package (mine was 3/4 cups water to 1/2 cup quinoa). Set aside to cool to room temperature.
In a bowl, combine mayonnaise and Sriracha. Mix in the marinated tuna into the spicy mayonnaise.
For assembly, place a handful of arugula on the bottom of a bowl, top next with the quinoa, red onions, tuna, scallions, and nori strips.