When you mention "sushi" vegetarian and vegan options may not be the first ones to come to mind, but they are common and offer a refreshing dining experience.
Natto (fermented soybeans)
High in protein and health benefits, natto can be enjoyed in two common sushi styles: gunkan-maki (battleship) and te-maki (hand rolled). Gunkan-maki is easy to devour and aesthetically pleasing, with the natto sitting on top on a pillow of sushi rice and wrapped with nori (seaweed) around its side. The te-maki variation allows you to customize your fillings in a larger, hand-sized, piece of nori. Spring onions and other tangy vegetables are a good complement to the natto.