Cut daikon and carrot into thin quarter slices. Slice green onion thinly.

Cut yellowtail into bite-sized pieces and pour boiling water over it using a strainer.

In a pot, heat water and dashi powder over medium heat. Once boiling, add daikon and carrot, cover, and simmer on low heat for 2–3 minutes.

Add yellowtail and green onion to the pot. Bring to a boil again, cover, and cook for 1 minute until the fish is cooked through.