Gather the ingredients.
Boil somen noodles in a large pot, according to the package instructions.
Drain and wash the noodles in water. Set aside.
Put dashi soup stock in a medium pot.
Bring it to a boil. Add soy sauce, salt, and mirin.
Put boiled somen in the soup and bring to a boil.
Stop the heat.
Sprinkle chopped green onion on top.
Serve and enjoy!