Rinse the rice cakes under running water.
Cut the fish cake and onion into bite-sized pieces.
In a pan, bring water, gochujang (Korean red chili paste), gochugaru (Korean chili powder), sugar, and soy sauce to a boil.
Add the rice cakes, fish cake, and onion, and simmer over medium heat.
When the rice cakes soften, add scallions and bring to a boil once more.