Prepare the rice according to directions on the package. Once cooked, set rice aside in a mixing bowl and season with salt and rice wine vinegar to taste. Allow rice to cool to room temperature.
In a bowl mix the mayo, sriracha, and 1/4 of the crab. Season with salt and pepper to taste. Set aside.
Dampen your hands with water (to prevent the rice from sticking), portion and spread the rice on the nori sheets. Covering as much of the nori as possible evenly. (Leave about 1 inch along the top and bottom of the nori sheet uncovered, as this will be how you seal your roll. Carefully flip the nori over onto a bamboo sushi mat or (piece of plastic wrap on top of a towel) so that the rice side faces down and the nori side faces up).
Lay the crab, cucumber, and avocado across the middle. Curve the rest of your fingers over the bamboo mat and gently press along the length of the "log." This motion presses the rice and the filling together and prevents the roll from being too loose. Pull the edge of the bamboo toward you to fold it underneath your hands (as shown in the picture), then continue to roll the sushi away from you until you've rolled past the far edge of the seaweed sheet.
Once rolled, gently press and form the length of the roll to make sure its compact and tight.
Slice the sushi roll into 6-8 pieces (you may have to rinse or wipe the blade in between slices to prevent sticking and tearing).
Top the roll with spicy crab salad. Drizzle with some more spicy mayo if desired. Garnish with sesame seeds.