Cut the radish into cubes to prepare the radish kimchi (kkakdugi).
Finely chop the onion and green onion.
Heat cooking oil in a pan and stir-fry the radish kimchi and onion.
Add tuna and stir-fry together.
Add chili powder and minced garlic, and stir-fry for a bit longer.
Pour in water or broth and bring to a boil.
When the soup boils, add the soft tofu and gently stir.
Season with salt or soy sauce (for soup) to taste.
Add green onion, bring to a boil again, and finish.