Squeeze the lemon juice over the avocado to prevent browning. Cut the Nori sheets in half. Lay a sheet of Nori, shiny side down, on a plastic covered mat. Wet your fingers with water and spread one half cup of the Botan Sushi Rice onto the Nori sheet and sprinkle with sesame seeds. Turn the sheet of Nori over so that the rice side is down. Place some each of the cucumber, avocado and shredded crab in the center of the sheet. Grab the edge of the mat closest to you, keeping the fillings in place with your fingers, and roll it into a tight roll using the mat to shape the roll. Pull away the mat and set roll aside. Cover with a damp cloth. Repeat until all of the Botan Sushi Rice and other ingredients have been used. Cut each roll into 6 pieces. Serve with wasabi and soy sauce.