Season the rice: Place the warm cooked sushi rice in a bowl. Add the sushi vinegar, sugar and salt, then gently mix until evenly combined. Set aside to cool slightly.
Prepare the nori: Place one sheet of nori on a clean work surface. Make a single cut halfway from one edge towards the centre of the sheet.
Add the fillings: Arrange the seasoned rice, avocado, tomato and ham in the four quarters of the nori sheet, keeping each ingredient in its own section.
Fold the onigirazu: Fold each quarter neatly over the next, working around the sheet until the fillings are completely enclosed. Press gently to secure.
Slice: Carefully cut the onigirazu in half to reveal the layered filling. Repeat with the second sheet of nori and remaining ingredients.
Pack the lunch box: Sprinkle the onigirazu with furikake and place them into a lunch box alongside your choice of fresh fruit, Baumkuchen and panda cookies.