Rinse the sushi rice under cold water until the water runs clear. Combine the rice and water in a rice cooker or pot and cook according to the rice cooker's instructions or bring to a boil, then reduce heat to low, cover, and simmer for 20 minutes. Remove from heat and let it sit, covered, for 10 minutes.

In a small saucepan, combine rice vinegar, sugar, and salt over low heat until dissolved. Once the rice is done, transfer it to a large bowl and gently fold in the vinegar mixture. Let the rice cool to room temperature.

In a separate bowl, mix the chopped shrimp, imitation crab meat, mayonnaise, sriracha sauce, and sesame oil until well combined.

Place a bamboo sushi mat on a clean surface and lay a sheet of nori, shiny side down. Wet your hands to prevent sticking, then spread about 1 cup of sushi rice evenly over the nori, leaving a 1-inch border at the top.

Arrange a line of the shrimp and crab mixture, avocado slices, and cucumber along the bottom edge of the rice-covered nori.

Using the bamboo mat, carefully roll the sushi away from you, pressing gently but firmly to keep the roll tight. Seal the edge of the nori with a little water.

Repeat the process with the remaining nori sheets and filling ingredients. Once all rolls are made, slice each roll into 6-8 pieces using a sharp knife.

Sprinkle tempura flakes on top of each roll for added crunch. Serve with soy sauce, pickled ginger, and wasabi.