Mix together the tuna, mayonnaise and soy sauce in a bowl until well combined.

To roll the sushi, cover a bamboo sushi rolling mat with plastic wrap. Sprinkle with toasted sesame seeds.

With wet fingers, firmly pat a thick, even layer of seasoned sushi rice on top of the rolling mat.

Place the cucumber in a line along the bottom edge of the sheet, then spread a line of tuna mixture alongside the cucumber.

Pick up the edge of the bamboo rolling sheet and fold the bottom edge of the sheet up to enclose the filling. Tightly roll the sushi into a thick cylinder.

Once the sushi is rolled, gently squeeze to compact it tightly.

Repeat to make a second roll.

Cut the rolls with a very sharp knife into 5 or 6 pieces each and serve them with soy sauce, pickled ginger and wasabi on the side.