Cook the sushi rice and set aside to cool.
Once the rice has cooled, stir the vinegar through, the rice should be sticky.
Cut the ends of the cucumbers off to ensure the thickness is consistent – this will make it easier to fill. Then cut the cucumber into half or in 10cm long chunks.
Using a teaspoon, swivel peeler or apple corer hollow out the centres of the cucumber until all the soft seed, area is scooped out. There should be about 4mm thickness of cucumber skin left.
Keeping the cucumber in a vertical position flat against the chopping board, stuff about 2 teaspoons of cooked rice into the cavity, using your fingers or teaspoon. Then use a knife or a wooden skewer to press the rice to one side of the cucumber. This will make way for the other veggies.
Slide in a few slices of capsicum and carrot into the cucumber and then fill with tuna until the cavity is full.
Cut each cucumber roll into sushi length slices (~2cm) or leave is as a sushi roll (~10cm).
Serve with salt-reduced soy sauce.
Serving Size 60-80g (8-10 slices)