Rinse 2 cups of sushi rice under cold water until the water runs clear. Cook according to package instructions, about 20 minutes. Mix in rice vinegar, sugar, and salt while warm.

Wash and slice the cucumber and avocado into thin, uniform strips, about ¼ inch wide.

Prepare your workspace by placing a bamboo sushi mat covered with plastic wrap. Lay a nori sheet shiny side down, positioned horizontally.

Using wet hands, take about 1 cup of cooled sushi rice and spread it evenly over the nori, leaving about 1 inch free at the top.

Place cooked shrimp or crab meat, cucumber, and avocado in the center of the rice-covered nori. Drizzle with sriracha sauce.

Lift the edge of the bamboo mat closest to you and roll it away from yourself, tucking the filling tightly. Form a cylindrical shape.

Slice the roll into eight equal pieces using a sharp knife dipped in water. Serve with soy sauce and an extra drizzle of sriracha.