Cut the rice cakes and fish cakes into bite-sized pieces.
Slice the onion and green onion thinly.
Pour water into a pot and add gochujang (Korean chili paste), gochugaru (chili powder), sugar, soy sauce, and minced garlic to make the sauce.
When the sauce starts to boil, add the rice cakes and fish cakes and simmer.
Once the rice cakes are soft, add the onion and green onion and cook a bit longer.
When the sauce thickens, turn off the heat, transfer to a bowl, and serve.