Cut rice cakes, fish cakes, and onion into bite-sized pieces.
Pour water into a pot and bring to a boil.
Add rice cakes, fish cakes, and onion to the boiling water.
Add gochujang (red chili paste), chili powder, sugar, soy sauce, and stir well.
Simmer over medium heat until the sauce thickens.
Slice green onion and add, then boil once more.
Serve the finished tteokbokki in a bowl.