Cut both sheets of nori in half. Lay one piece of nori shiny side down, on a bamboo mat covered in plastic wrap. Spread about ¾ cup of rice evenly on the nori sheet.
If needed, wet hands to help spread the rice. If desired, sprinkle with ½ tablespoon of white or black sesame seeds, making sure they adhere to the rice.
Flip the nori over (rice side facing down). Place a few slices of carrot and cucumber along the bottom of the nori. Add a few slices of avocado right above.
Grab the nori and the rolling mat. Fold the nori over until it touches itself. Continue rolling until a complete roll is formed. Squeeze gently, but firmly. Repeat with remaining 3 nori sheets.
Transfer to a cutting board. With a very sharp knife, slice roll into 8 slices. Wipe knife on a damp cloth in between each cut to keep the rice from sticking. Serve immediately with wasabi and pickled ginger.