1. On a bamboo mat place a 1/2 sheet of nori smooth side down, rough side up. Using 3 to 4 ounces, spread rice lightly across the rough side, completely covering the seaweed. If desired, sprinkle sesame seeds across the rice.
2. Flip the nori over so the smooth side of the seaweed is facing up. You can line the mat with plastic wrap if you prefer.
3. Place a few pieces of cucumber and avocado lengthwise and add crab. Make sure you squeeze any liquid out of the crab to avoid a soggy roll.
4. Using the bamboo mat, begin to tightly roll the sushi. Start at the side closest to you and roll away from yourself. Make sure your hands are damp; if you touch the rice you don't want it sticking to your hands.
5. Using a very sharp knife, cut roll into 8 pieces. Serve with wasabi and sodium-reduced soy sauce.