Prepare the sushi rice. In a medium bowl, whisk together mayonnaise and sriracha. Once combined, add in cubed tuna. Cover, and allow to marinate in the refrigerator while preparing the other ingredients.
Transfer to a cutting board. With a very sharp knife, slice roll into 8 slices. Wipe knife on a damp cloth in between each cut to keep the rice from sticking. Serve immediately with wasabi and pickled ginger.