Soak the sliced rice cakes in cold water for 10 minutes.
Cut the fish cake into bite-sized pieces.
Thinly slice the onion and green onion.
Heat cooking oil in a pan and sauté the onion and green onion.
Add the fish cake and stir-fry together for 2 minutes.
Add the rice cakes and stir-fry for another 2 minutes.
Add soy sauce, gochujang, sugar, and water. Mix evenly and stir-fry for 3 minutes.
Finish with sesame seeds and pepper.