Rainbow Rolls

Place rice in a large bowl; add enough cold water to cover rice by 1 inch. Let soak for 15 minutes. Drain rice in a fine mesh strainer. Rinse rice under cold water, agitating grains with your hand to release starch, until water runs clear, 2 to 3 minutes. Transfer rice to a medium saucepan, and add 2 cups water. Bring to a boil over high. Reduce heat to low; cover and cook until rice absorbs water, about 15 minutes. Remove from heat; let rice stand, covered, for 10 minutes. (You will have 4 cups cooked rice).

While rice cooks, stir together mayonnaise, togarashi, mirin, and salt in a small bowl. Add crabmeat, and toss to coat. Set aside.

Transfer cooked rice to a baking dish (such as a 13- x 9-inch baking pan) or a large bowl; drizzle with 1 tablespoon of the vinegar. Using a rice paddle, fold rice from outer edges into the center, and gently fluff. Be careful not to smash the rice; simply break apart the clumps. Repeat drizzling, folding, and fluffing process with remaining 3 tablespoons vinegar. Cover with a damp towel, and let cool to room temperature, about 15 minutes.

Meanwhile, slice fish fillets across the grain into 1/8-inch-thick slices. Slice 1 avocado into 1/4-inch-thick slices for the inside of the roll; slice remaining avocado into 1/8-inch-thick slices to drape across top of the roll. Place in refrigerator until ready to use.

Cover or wrap a 9 1/2-inch bamboo sushi mat with plastic wrap, and place on a clean work surface. Fill a small bowl with warm water, and place next to work area. Place 1 nori sheet on bamboo mat, aligning the lines on the nori with the threads of the mat running crosswise. Scoop about 1 cup prepared rice onto nori sheet. Dampen hands with warm water; gently press rice into an even layer over nori, completely covering edges of nori. Sprinkle evenly with one-fourth of the black and white sesame seeds (about 3/8 teaspoon each). Carefully flip nori sheet over so that the rice is touching the plastic wrap and nori sheet is facing up. Arrange 6 to 8 cucumber pieces lengthwise along bottom third of the nori sheet. Top with about 2 tablespoons crabmeat mixture and 2 or 3 of the 1/4-inch-thick avocado slices. Using the bamboo mat and plastic wrap, lift and roll the bottom of sushi-nori sheet up and over filling, tucking the bottom of nori around filling and gently pulling and pressing on the bamboo mat. Continue to roll/tuck/press in quarter-turn increments until filling is tightly enclosed by the sushi-nori sheet. Firmly hold, pull, and gently tighten the bamboo-wrapped sushi roll to seal. Remove bamboo and plastic wrap from sushi roll. Wipe down plastic-wrapped mat with a paper towel, or replace plastic wrap (it will make nori soggy and hard to work with if it gets too damp). Repeat process 3 times to make 4 sushi rolls total.

Arrange fish slices and reserved 1/8-inch-thick avocado slices evenly among the tops of sushi rolls, arranging pieces diagonally overlapping slightly, and alternating pieces.

Wet a clean kitchen towel with hot water. Wipe your sharpest knife with a wet towel, and cut each sushi roll into 6 to 8 slices, wiping knife between each cut to ensure a clean cut. Serve sushi rolls with pickled ginger, wasabi, and soy sauce.