Cold somen noodles with sliced lemon and salted green onions.
Slice 1/2 lemon thinly and set aside. Squeeze the other 1/2 lemon into a small bowl. Add the thinly cut green onions, salt, and garlic powder to the lemon juice and mix well. Mix the mentsuyu sauce with cold water and set aside.
Boil the somen noodles according to the package instruction (about 2 minutes.) Strain and wash the somen noodles in running water. Add the ice to the strainer to chill the noodles.
Serve the somen noodles in a bowl and top with the lemon slices and the salted green onions. Pour the mentsuyu sauce.