To Prep To begin, cut the avocados in to halves, pit and then peel off the skin. Pour the lemon juice over avocados to prevent browning and then cut in to thick strips. Cut the cucumber in to thin long strips, and slice to remove cucumber seeds.To assemble the sushiWrap the bamboo mat used to fold sushi with cling film to make cleaning easier and to stop rice granules from getting stuck on the mat. On the mat, place one seaweed sheet down and spread about 1 cup of rice evenly onto the nori sheet. Use your fingers to press and push to rice to form an even layer of rice.Turn the sheet over so that the rice now faced down on the bamboo mat. Arrange the avocado and cucumber in a row, close to the bottom of the sheet.Then, pull up the bottom edge of the mat, while using your fingers to roll and tuck the fillings in. Lift the mat slightly to go over the roll, and continue rolling forward while keeping a firm hold.Remove the roll from the mat and place on to a section of cling wrap and sprinkle the rice with the sesame seeds. Roll the cling wrap over the roll to full coat the rice. Remove the roll from the cling wrap and the use a sharp knife to cut the roll into equal portions.