Prepare a bowl of cold water to wet your hands. (This will prevent the rice from sticking to your fingers)
Mix the mayonnaise and wasabi.

For the sushi rice:
Dissolve the sugar in the rice vinegar.
In a fine mesh sieve, rinse the rice under cold running water until the water is clear.
In a saucepan, weigh the rice and add 1.5 times its volume in water. Bring to a boil and cook for 15 minutes over low heat and covered.
Let the rice cool down.
Pour the sugar-vinegar mixture over the rice and mix with a bamboo spatula. Lay a bamboo mat or a plastic food wrap on a work surface.
Place a thin and even layer of rice on the surface.
Cut a sheet of nori seaweed. Flip it over to have the rice facing you.
Draw a line of wasabi mayonnaise across the width.
Place the pieces of salmon and cucumber. Sprinkle generously with tempura.
Roll it up, closing the roll as you go.
Sprinkle with sesame seeds. Refrigerate until serving.