Run a fork lengthwise along your imitation crab to shred it. Place the crab in a small bowl alongside the mayonnaise, sriracha, salt, white pepper, and granulated sugar. Mix to combine. This is your Kani Salad.
Wrap your sushi mat in plastic wrap so that the rice does not stick to the bamboo. Put the ½ seaweed sheet on the mat with the rough side up.
Press ½ cup of cooked sushi rice across the entire ½ nori sheet, then sprinkle the rice with black sesame seeds. Flip the seaweed over so the smooth side is showing.
Lay a thin line of Kani Salad across the center of the seaweed.
Place a thin line of cucumber slices next to the Kani Salad on one side, and a thin line of avocado slices next to the Kani Salad on the other side.
Place your thumbs under the sushi mat. Then lift the edge of the mat closest to your belly up and over the filling in the center.
Use your hands to press the length of the log, making sure that all of the sushi ingredients are staying together. Continue lifting and rolling the edge of the sushi mat until the sushi is in one roll. Gently press with your hands again to make sure that the rice on the outside edge is sticking together.
Remove the mat and use a knife to cut the sushi into 8 pieces. Serve and enjoy!