Thoroughly rinse rice. Bring water and rice to a boil in a saucepan over high heat. Reduce heat to medium-low, cover, and simmer until the rice is tender and the liquid has been absorbed 20 to 25 minutes. Place cooked rice in a large bowl. Mix vinegar, sugar, and salt in a small saucepan and heat in on a stove until the sugar and salt dissolve in the vinegar. Add the mixture to the rice. Fold and cut the rice with a rice spatula to make sure the mixture is applied evenly. Do not stir. Cool rice to room temperature.
Place a sheet of nori on a flat work surface. Spread a thin layer of rice on top of the nori. Top of with avocado slices, crab mixture and cucumber strips on the other side. Using the mat as a guide, carefully roll the California roll into a tight log. Remove the rolling mat. Cut the roll into 6 or 8 even pieces using a wet knife. Repeat with remaining sheets of nori and filling.
Serve garnished with pickled ginger, soy sauce, and wasabi paste. Enjoy your meal!!!