Soak the rice cakes in cold water for 10 minutes.
Cut the fish cake into bite-sized pieces.
Slice the onion and green onion thinly.
Pour water into a pot and add gochujang, chili powder, soy sauce, and sugar to make the sauce.
Add the rice cakes to the sauce and bring to a boil.
When the rice cakes turn soft, add fish cake, onion, and green onion, and boil further.
Once all ingredients are cooked, turn off the heat and transfer to a plate.