Rinse the rice: Place sushi rice in a bowl and cover with cold water. Swirl, drain, and repeat until the water runs mostly clear. This removes excess starch and helps the rice stay fluffy.

Cook the rice: Use a rice cooker or stovetop per package instructions. Aim for tender grains that hold their shape. Let it sit covered for 10 minutes after cooking.

Season the rice: Warm the rice vinegar with sugar and salt until dissolved. Transfer the hot rice to a wide bowl. Pour the vinegar mixture over and fold gently with a spatula to coat. Fan to cool until just warm and glossy.

Prep the vegetables: Slice cucumber and radishes into thin matchsticks. Pat them dry with a paper towel. Slice green onion if using.

Set up your station: Place the bamboo mat on a clean surface. Put the nori shiny side down with the short edge facing you. Keep a small bowl of water nearby to wet your fingers.

Spread the rice: With damp fingers, spread a thin, even layer of rice over about two-thirds of the nori, leaving a 1-inch strip at the top edge bare. Don’t pack the rice tightly.

Add fillings: Arrange a line of cucumber and radish matchsticks across the rice about 1 inch from the bottom edge. Add green onion and a sprinkle of sesame seeds.

Roll it up: Lift the edge of the mat closest to you and roll over the filling, tucking it gently to keep everything snug. Continue rolling until you reach the bare strip of nori.

Seal the roll: Wet the bare edge with a little water and finish rolling to seal. Give the roll a gentle squeeze with the mat to set its shape.

Slice: Use a sharp, slightly damp knife to cut the roll into 6–8 pieces. Wipe the blade between cuts for clean slices.

Repeat: Assemble and roll the remaining nori sheets and fillings.

Serve: Arrange on a platter. Sprinkle more sesame seeds on top if you like. Serve with soy sauce, wasabi, and pickled ginger.