Cut the rice cakes and fish cakes into bite-sized pieces.
Add water, gochujang (Korean chili paste), chili powder, sugar, and soy sauce to a pan and bring to a boil.
When the sauce is boiling, add the rice cakes and fish cakes and continue to boil.
Add onion and green onion, then simmer over medium heat, stirring occasionally.
Once the rice cakes are soft, it's ready to serve.