Cut the pollack into bite-sized pieces and rinse thoroughly.
Slice the onion, green onion, and garlic.
Add cooking oil to a pan and sauté the garlic.
Add the onion and green onion and stir-fry.
Make the sauce by mixing gochujang, soy sauce, red pepper powder, sugar, and water.
Place the pollack in the pan and pour the sauce over it.
Simmer over medium-low heat until the fish is cooked and the sauce reduces.
When there's a small amount of sauce left, turn off the heat and sprinkle with sesame seeds.