Mix the tuna, mayonnaise, and wasabi in a bowl until the mixture is smooth and evenly combined.

To roll the sushi, cover a bamboo sushi rolling mat with plastic wrap, then place a sheet of nori on top with the rough side facing up. With wet fingers, firmly press a thick, even layer of seasoned sushi rice over the nori until it is fully covered.

Arrange 2 slices of cucumber in a line along the bottom edge of the nori, then spread a line of the tuna mixture right beside the cucumber.

Lift the edge of the bamboo mat and fold the bottom section of the nori up and over the filling, then roll it forward tightly to form a compact cylinder.

After rolling, gently squeeze along the length of the mat to set and firm up the roll.

Repeat the rolling process to make the second roll.

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