Prepare Mentsuyu: Combine kombu dashi powder, mirin, soy sauce, salt, and water in a pot and bring to a boil. Let it cool before serving.
Cook Somen Noodles: Boil plenty of water (not in the ingredients list) in a medium saucepan. Add somen noodles, and cook according to the package instructions. Stir the noodles with chopsticks to separate them while cooking.
Drain the Noodles: Drain using a strainer and quickly rinse under cold running water to cool it down.
Serve: Place the drained somen noodles in a serving bowl, serve the mentsuyu in a separate small bowl, and accompany with chopped scallions and grated ginger.
Notes
When boiling somen, use plenty of water. This gives the noodles enough room to move freely and prevents them from sticking together.
After boiling, rinse the noodles immediately under cold running water to stop the cooking process and remove excess starch. This helps achieve a firm and chewy texture.
Somen noodles tend to stick together over time. Toss them gently with a little cold water or add ice cubes to the serving bowl to prevent this.