Slice 1/2 an avocado into long thin strips. Do the same with the cucumber.
Place one nori sheet on the rolling mat. Moisten your hands and grab a handful of rice. Using only two thirds of the nori sheet, pat the rice in to a layer no more than 1/3 of an inch thick.
Take the avocado and place it in a horizontal line on the rice, making sure to stretch from one end of the mat to the other.
Repeat this using the cucumber. The less filling you use, the easier it is to roll.
Gently roll the sushi toward the seaweed only side using the mat. Once you near the end, use a bit of water and pat the nori to seal the roll. Then, just slice your roll into 1 inch pieces using a sharp knife.