Cut the kimchi into bite-sized pieces.
Slice the onion and green onion.
Add sesame oil to a pot and stir-fry the kimchi.
Add red pepper powder and stir-fry together.
Pour in water or broth and bring to a boil.
Add tuna and boil.
Add onion and green onion, and boil for a little longer.
Taste and if needed, season with salt or soup soy sauce.