Step 1Rinse the rice under cold running water 2 or 3 times; drain in a strainer for about 20 minutes.
Step 2Combine the rice and water in a saucepan. Bring to a boil, reduce the heat to low. Simmer, covered, until the rice is tender and the water has been absorbed, 20 minutes.
Step 3Combine the vinegar, sugar and salt in a bowl. Set aside.
Step 4Transfer the hot rice to a bowl and quickly toss with the vinegar mixture.
Step 1Place a sheet of seaweed shiny side down on a bamboo mat, with the long edge toward you. Moisten your hands with water and spread a cup of Sushi Rice about 1/8 inch thick evenly over the seaweed to the edges and the bottom and within 1 1/2 inches of the top. Across the center of the rice bed, dab a thin line of wasabi paste, about 1/4 teaspoon if you like your sushi hot.
Step 2Use 1/3 of the sushi fillings for each roll of sushi: Place some of the crab, if using, the avocado, carrot and cucumber lengthwise across the rice. Sprinkle with the sesame seeds. Then, holding the filling down with your fingers, lift up the mat with your thumbs and roll it over until the seaweed and rice form a tube. Press the bamboo-covered roll firmly to compress the roll enough to cut easily. Use the remaining ingredients to make 2 more rolls. The sushi can be refrigerated up to 4 hours.
Step 3To serve, wipe a sharp knife with a well-wrung damp cloth. Place a roll lengthwise on a cutting board and slice in half, crosswise. Cut each half into 4 pieces. Be careful not to saw back and forth, or else the roll will fall apart. Repeat with the remaining rolls. Place in the bento box. Put the pickled ginger in a cup or foil and put it next to the sushi.