Wash and dry the cucumbers thoroughly. Slice off the ends and cut each cucumber in half lengthwise.

Use a spoon to hollow out the center of each cucumber half to create a 'boat.' Be careful not to scrape too deep; leave a sturdy base for filling.

In a small bowl, combine the cooled sushi rice, rice vinegar, sugar, and salt. Mix well until the rice is seasoned evenly.

Fill each cucumber 'boat' with a layer of the seasoned sushi rice, packing it gently to hold its shape.

Layer thin slices of avocado, carrot strips, bell pepper strips, and optional nori pieces on top of the rice inside each cucumber half.

Gently press down the toppings to secure them in place. Slice each cucumber half into bite-sized pieces, approximately 1-inch wide.

Arrange the cucumber sushi pieces on a serving platter and serve with soy sauce and optional pickled ginger on the side.