• Gather all the ingredients.
  

To Poach the Chicken

• Slice 1 knob ginger into thin slabs and cut 2 green onions/scallions into 2-inch (5-cm) pieces.
  
• To a pot, add 4 cups water and ½ lb chicken breast.
  
• Next, add the sliced ginger and green onions to the pot. Finally, add 2 Tbsp sake and 1 tsp Diamond Crystal kosher salt.
  
• Bring the pot of water and chicken to a boil over medium heat. Once boiling, skim off the foam and scum.
  
• Now, lower the heat to low and cover the pot with the lid slightly ajar. Gently cook the chicken for 15 minutes.
  

To Prepare the Toppings

• In the meantime, peel the skin of 1 Japanese or Persian cucumber in stripes by alternating peeled and unpeeled strips down the length of the cucumber. Slice the cucumber thinly.
  
• Cut the sliced cucumber into julienned strips. Cut 1 tomato in half and thinly slice the halves. Transfer them to a plate.
  

To Make the Sesame Miso Sauce

• Grind 2 Tbsp toasted white sesame seeds with a mortar and pestle. Set aside.
  
• In a bowl or liquid measuring cup, combine 2 Tbsp miso, 1 Tbsp soy sauce, 1½ Tbsp rice vinegar (unseasoned), and 2 Tbsp sugar.
  
• Add the ground sesame seeds and 1 tsp toasted sesame oil to the bowl. Mix it all together until smooth.
  
• After 15 minutes of cooking the chicken, the poaching liquid is now a flavorful chicken stock. Reserve ⅓ cup chicken stock/broth and gradually stir it into the sauce ingredients until well combined. Set aside.
  

To Shred the Chicken

• Remove the chicken breast from the pot and shred it using two forks. Transfer it to the plate with the cucumber and tomato.
  

To Cook the Noodles

• Bring a pot of water to a boil. With your fingers, loosen and separate 2 servings hiyashi chuka noodles and add them to the boiling water.
  
• Cook according to the package instructions. When done, remove the noodles from the pot and plunge them into a bowl of iced water. This stops the cooking and chills the noodles.
  

To Serve

• Drain the chilled noodles well and serve them on individual plates. Place the toppings on the noodles and sprinkle with extra sesame seeds. Garnish with 1 sprig cilantro (coriander) (optional) and drizzle with the Sesame Miso Sauce before serving.
  

To Store

• You can keep the sauce and toppings in airtight containers separately, but I recommend preparing the noodles right before you serve. Store in the refrigerator for 3 days and in the freezer for a month.