Separately, dice tomato and cucumbers into 1⁄4 inch cubes. Combine into a mixing bowl. Slice onion thinly with the grain, then add to the same bowl. Mince jalapeño and add to the bowl. Rough chop cilantro and add to the bowl with the other contents.
Add fish, then toss to mix evenly. Squeeze citrus directly into mixture. Add vinegar and mix evenly.
Chill and allow fish to marinate in citrus for at least 1 hour or until the fish has firmed up and is no longer raw.
Once ready, season with salt to taste. Garnish right before serving with sesame, hand torn cilantro and a drizzle of olive oil.