Step 1Toss the chicken with the sake, onion and ginger in a shallow, heat-proof bowl large enough to hold the chicken.
Step 2Prepare a stove-top steamer and place the chicken, still in the bowl, on the rack in the steamer. Steam the chicken until the meat is cooked through; it will be firm and opaque and the juices will run clear, 20 to 25 minutes.
Step 3Remove from heat and cool the chicken in the bowl with the flavorings, then refrigerate the chicken, still in the bowl, until completely chilled. The chicken can be cooked up to 1 day ahead and refrigerated before shredding.
Step 4Shred the chicken into matchstick pieces about 3 inches long. Place the chicken in a medium bowl and toss with the sesame oil. Refrigerate the chicken, covered, until ready to use.
Step 1In a medium bowl, whisk together the ginger juice, sesame paste, sugar, sake, sesame oil, rice vinegar, soy sauce and water. Add the tobanjan or the la yu, a little at a time as desired (add the tobanjan one-eighth teaspoon at a time to taste, and the la yu a few drops at a time to taste), mixing and tasting until the desired heat is achieved. Strain if desired for a smoother sauce. Refrigerate, covered, until needed.
Step 1Break the eggs into a small bowl and stir together.
Step 2Heat a medium nonstick frying pan over medium-high heat and add 1 teaspoon oil. Reduce the heat to low and gently add half of the egg to the pan, tilting the pan to form a large, thin crepe. Cook quickly and gently, careful not to burn (it should be completely yellow) but cooking until the egg is set and cooked through. Remove the crepe to a cutting board to cool slightly. Repeat with the remaining oil and egg.
Step 3When the first crepe is cool enough to handle, halve it to make two moons. Trim the edges to form each half into a rectangle about 3 inches wide. Cut each rectangle crosswise into matchsticks one-eighth inch wide. Set the sliced egg aside and repeat with the remaining crepe. Cover and refrigerate until needed. The egg can be prepared and refrigerated a few hours in advance.
Step 4Cook the somen: Bring a large pot of water to a boil and add the noodles, spreading them apart so they do not stick together while cooking. When the water returns to a boil, add half-cup tap water. Cook the noodles until they are al dente, about 3 minutes total cooking time. Immediately remove from heat.
Step 5Drain the noodles and cool them in a large bowl of water under running tap water. Gently swirl the noodles in the running water until the water runs clear. Drain the noodles again.
Step 6Place the noodles in a large bowl. Add the ice and enough water to mostly cover the noodles. Chill the noodles for at least 3 to 5 minutes before serving. The noodles will dry out rather quickly after they are removed from the water so try to keep the noodles in the water until just before serving.
Step 7When ready to serve, remove the noodles from the ice water and strain lightly. Make a bed of noodles on an oblong platter. Arrange the chicken, cucumber, carrot, green pepper and the egg matchsticks around the noodles. Garnish with chives, daikon radish sprouts, shiso leaves (one or all of them) and the roasted sesame seeds.
Step 8Let each person help themselves to the noodles. You can use small serving dishes. Toss the noodles, chicken and vegetables together and serve in individual dishes. Pass the ginger sesame sauce around. You only need two or three teaspoons to season each serving.