For the pickled ginger, place the sugar and vinegar into a small saucepan and heat gently until the sugar is dissolved. Remove from the heat, add the sliced ginger and stir to coat. Set aside and allow to cool for five minutes.
For the maki rolls, lay the nori sheet on a bamboo sushi mat. Spread the rice over two-thirds of the sheet, leaving a 1cm/½in border at the top.
Spread the tuna strips and cucumber sticks lengthways across the sheet, then place the avocado slices on top.
Brush the border with vinegar and roll the nori sheet up very tightly over the filling using the bamboo mat, to make a cigar shape, sealing across the border at the top.
To serve, slice the roll into rounds and place onto a serving plate with the pickled ginger.
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