There are dozens of variations of sushi, each with different ingredients and ratios, but here is some info that you can apply to the roll in front of you.

Sashimi: Shehakol

On one extreme, we have sashimi, which is just fish, commonly salmon or tuna. The blessing on sashimi is Shehakol the catch-all blessing for fish, meat, cheese, eggs and other foods that are not plant-based.

Sushi: The Rice Question

One can argue that the primary ingredient in sushi is rice. In fact sushi is Japanese for “sour rice.” So what blessing do we say before eating rice? For reasons you can read here, there are different traditions regarding this question. The upshot is that the Chabad practice is to either eat rice as part of a bread-based meal (when no blessing at all is needed) or to say the catch-all blessing of Shehakol.

The Veggie Roll

If you like your sushi overflowing with vegetables (or fruit like avocado), to the point that the roll contains mostly vegetables, the blessing would reflect that of its content: Ha’adamah for cucumber, carrot, etc, and Ha’etz for avocado.