Prepare sushi rice according to the recipe instructions and let cool to room temperature.
Wrap the bamboo mat in plastic wrap; this prevents the rice from sticking to the mat and makes clean-up easier. Cut the whole nori sheet in half using scissors to make two half sheets.
Place a half sheet of nori on your bamboo mat horizontally, with the shiny side facing down (rough side facing up). Wet your fingers in a small bowl of water. With wet fingers, grab some sushi rice and evenly spread it out on your nori sheet, leaving about 1/2 inch of the top portion of the nori uncovered.
Optional to include wasabi in your sushi rolls, dab a little bit on your finger and then gently spread it horizontally down the center of the sushi rice. Add an even layer of your julienned cucumbers then top with crushed sesame seeds.
Roll sushi by lifting the edge of the bamboo mat closest to you and folding it over the filling. Hold the filling with your other hand and roll it tightly away from you, pressing down on the roll. Dip your finger in water, wet the uncovered nori with water to act as glue, finish rolling, and press firmly with both hands to ensure it holds together.
Cut the sushi roll into six pieces with a slightly wet, sharp knife using a back-and-forth motion. You can use a ruler to help you get evenly sized pieces. Enjoy immediately with soy sauce for dipping.