Soak rice for 4 hours. Drain rice and cook in a rice cooker with 2 cups of water until cooked and water absorbed. Remove from heat and immediately stir rice vinegar through the hot rice. Spread rice on a plate and leave until completely cool.
Place 1 sheet of seaweed on bamboo mat and spread a thin layer of cool rice on top, leaving about 1 cm of the seaweed uncovered at the top and bottom edge. This will make sealing easier later.
Dot a little wasabi across the rice and arrange cucumber, avocado and smoked salmon in a line on top, about 2.5cm from the bottom edge of the seaweed.
Roll tightly from bottom to the top edge, with the help of the bamboo mat, dampening the top edge of the seaweed and pressing to seal. Repeat for remaining ingredients.