Begin by washing the sushi rice in a sieve under cold water until the water runs clear.
Cook the rice with the water in a rice cooker or pot, following the manufacturer's instructions or typical rice cooking methods.
Once cooked, transfer the rice to a large bowl. Gently fold in the seasoned rice vinegar, sugar, and salt with a paddle or spoon while the rice is still warm.
Lay a sheet of nori on a bamboo sushi mat. With dampened hands, press an even layer of sushi rice onto the nori, leaving about an inch of space at the top.
In a small bowl, mix the crab meat with mayonnaise. Spread this mixture across the center of the rice.
Add a row of avocado slices on top of the crab mixture. If desired, squeeze a bit of lemon juice over the avocado to enhance the taste.
Carefully start rolling the mat from the edge nearest to you, keeping the fillings in place with your fingers, and roll tightly.
Wet the top edge of the nori with a little water to seal the roll.
Use a sharp knife to slice the roll into six or eight pieces, wiping the knife with a damp cloth between cuts to clean the blade.
Serve the California roll with soy sauce, pickled ginger, and wasabi. Enjoy your homemade sushi!