01 - Rinse sushi rice under cold running water until the runoff becomes completely clear. Transfer the rice and 2½ cups of water to a medium saucepan, bring to a rolling boil, then cover with a tight-fitting lid. Reduce heat to low and simmer for 15 minutes. Remove from heat and let the rice steam, still covered, for an additional 10 minutes.
02 - Combine rice vinegar, sugar, and salt in a small saucepan over low heat, stirring until the sugar and salt have fully dissolved. Transfer the cooked rice to a large non-metallic bowl, pour the vinegar mixture over it, and fold gently using a cutting motion while fanning the rice to bring it to room temperature. Avoid mashing the grains.
03 - Shred or cut the imitation crab sticks into thin strips. Place in a bowl and fold in the Japanese mayonnaise until evenly coated. Set aside.
04 - Place a bamboo sushi mat on a flat work surface and cover it tightly with plastic wrap. Lay one sheet of nori shiny side down on the mat. With damp hands, spread approximately ½ cup of seasoned sushi rice in an even layer across the nori, leaving a ¾-inch border along the top edge.
05 - Sprinkle tempura flakes and toasted sesame seeds evenly over the rice. Carefully flip the nori sheet so the rice side faces down on the plastic-wrapped mat.
06 - Arrange a horizontal line of the crab-mayonnaise mixture, sliced avocado, and julienned cucumber along the bottom edge of the nori, about 1 inch from the bottom.
07 - Using the bamboo mat as a guide, roll tightly from the bottom edge upward, tucking the fillings firmly inward as you go. Apply gentle even pressure along the length of the roll to seal the seam. Let the roll rest seam side down for 1 minute before slicing.
08 - Wipe a sharp knife with a damp cloth. Slice each roll into 6 even pieces, wiping the blade clean between cuts for neat edges.
09 - Sprinkle additional tempura flakes over the top of each sliced piece for extra texture.
10 - Arrange the pieces on a platter and serve accompanied by soy sauce, pickled ginger, and wasabi paste on the side.