Nori-rolled sushi

1 cup rice
4 tbsp white vinegar
1 tbsp sugar
1 tsp salt
1/2 cucumber, seeded
1 avocado
6 oz fresh tuna or salmon
4 sheets nori seaweed
1 tsp wasabi paste
Pickled ginger, to serve
Soy dipping sauce

1. Begin by cooking the rice. Wash it well in warm water, then place in a pan. Cover with water so that it comes 3/4 inch above the rice. Cover and cook gently for 12 minutes, or until the rice is tender and the water has been absorbed.
2. Meanwhile, mix together the vinegar, sugar, and salt and set aside to dissolve. As soon as the rice is cooked, stir the vinegar mixture into it and leave to cool.
3. Cut the cucumber, avocado and fish into strips.
4. Halve the nori sheets and place one half horizontally on the rolling mat. Spread 2-3 tbsp of the rice mixture on the seaweed, leaving a 1/2 inch margin on the edge furthest from you.
5. Spread a tiny amount of the wasabi across the center of the rice, then place a row of cucumber and avocado or fish across the center. Roll up so the seam is on the bottom of the roll. Continue to make rolls, alternating the ingredients so that some contain just fish and others contain cucumber and avocado.
6. Trim the ends of the rolls with a sharp knife, then cut each into six pieces. Transfer to serving dishes and serve with a spoonful of pickled ginger and Soy Dipping sauce.