Cut the rice cakes and fish cakes into bite-sized pieces.
Add water and gochujang (Korean chili paste) to a pan and bring to a boil.
Add onion, green onion, rice cakes, and fish cakes. Simmer over medium heat.
Add sugar, soy sauce, and chili powder, and mix well.
Stir occasionally and simmer until all ingredients are cooked through.
Transfer the finished tteokbokki to a serving dish.