Begin by rinsing the sushi rice under cold water until the water runs clear. This removes excess starch and prevents the rice from becoming too sticky.

Combine the rinsed sushi rice and 2.5 cups of water in a medium saucepan. Bring to a boil, then reduce the heat to low, cover, and simmer for about 20 minutes, or until the water is absorbed and the rice is tender.

While the rice is cooking, combine the rice vinegar, sugar, and salt in a small saucepan. Heat over low heat until the sugar and salt are dissolved. Remove from heat and let it cool slightly.

Once the rice is cooked, transfer it to a large bowl and gently fold in the vinegar mixture while the rice is still warm. Allow the rice to cool to room temperature.

Lay a bamboo sushi mat on a flat surface and place a sheet of nori on top, shiny side down. Wet your hands to prevent sticking, and spread approximately 1/2 cup of the prepared sushi rice evenly over the nori, leaving a 1-inch border at the top edge.

Arrange a few strips of julienned cucumber and carrot horizontally along the center of the rice layer.

Using the bamboo mat, carefully roll the sushi away from you, pressing firmly to ensure the roll holds its shape. Continue rolling until you reach the border. Seal the roll by moistening the edge with a little water.

Repeat the process with the remaining ingredients to make a total of 4 rolls.

Using a sharp knife, slice each roll into 6 equal pieces. Wipe the knife with a damp cloth between cuts to ensure clean slices.

Serve the vegetable sushi rolls with soy sauce for dipping.