Cut rice cakes and fish cakes into bite-sized pieces.
Slice onion and green onion thinly.
In a pot, add water, gochujang (Korean chili paste), red pepper powder, sugar, soy sauce, and minced garlic, then bring to a boil.
Once the sauce starts boiling, add the rice cakes, fish cakes, and onion.
Boil over medium heat until the rice cakes become soft.
Add the green onion and let it simmer briefly at the end.
Serve on a plate to finish.