Rinse sushi rice under cold water until clear. Cook according to package instructions, typically around 20 minutes. Transfer to a large bowl and fold in rice vinegar, sugar, and salt while warm.

Slice cucumber and avocado into thin strips, about ¼ inch thick. Shred or slice shrimp or crab meat into bite-sized pieces for easy rolling.

Lay a bamboo sushi mat on a flat surface and cover it with plastic wrap. Place a nori sheet shiny side down, slightly centered.

With wet hands, spread 1 cup of seasoned sushi rice evenly over the bottom two-thirds of the nori sheet.

Place protein, cucumber strips, and avocado slices in a line across the center of the rice-covered nori. Drizzle sriracha sauce for a spicy kick.

Lift the edge of the mat closest to you and roll away, tucking the nori under. Continue rolling until the top edge of the nori reaches the rice, sealing with water.

Slice the roll into 8 equal pieces using a sharp, wet knife. Arrange on a platter and serve with soy sauce and extra sriracha.