Add the sake, salt, and 3 cups of water to a small sauce pan and bring to a boil. Add the chicken, and when it comes to a boil again, reduce to low heat for 3 minutes.
Remove the chicken and quickly rinse in cold water. Once it cools to the touch, tear it into thin strips. (Remove any tough bits.)
Thinly slice the tomato. Thinly slice the cucumber diagonally, then cut them into thin strips.
Make the sauce. After thoroughly mixing all the ingredients listed from the ginger up to the soy sauce, add the ra-yu and sesame oil and lightly mix.
Arrange the tomatos, cucumbers, and chicken on a plate, and top with the sauce before serving.
Story Behind this Recipe
I came up with a delicious sauce recipe. It's pretty spicy, so if you don't like spice, use half the amount of ra-yu. This recipe makes plenty of sauce. If you have leftover sauce, put it in the fridge and use it for Chinese food, boiled eggs, or on salads.
You could use the water in which you boiled the chicken as soup broth. I hear it's also delicious if you use peanut butter instead of white sesame paste, making it slightly less sweet.