Rinse sushi rice and cook with a ration of 1 cup of rice to 1.5 cups of water. Add a tablespoon of rice wine vinegar and sugar. Spread cooked rice over a sheet pan and refrigerate to cool quickly. 

Dice cucumbers, green onions, avocado, and seaweed sheets. Lay everything out to make an assembly line.  Layer rice, crab salad, and toppings in a bowl. Add soy sauce or sriracha to taste.