Mix the ingredients together well in a bowl.
Cut the kimchi into small pieces. Thinly slice the cucumber diagonally, then cut into thin strips. Cut the thin green onions the same size as the cucumbers.
Boil the soumen according to the directions on the package. Cool with cold water, then drain well.
Put the soumen and the vegetables from Step 2 into the bowl from Step 1 and mix well. Transfer to a plate and optionally top with a boiled egg. Sprinkle on some lemon juice.
If you don't have any mentsuyu, mix together 2 tablespoons of soy sauce and 1 teaspoon of sugar to make some. You can also use some soumen dipping sauce or yakiniku sauce if you like.