Wash the soybean sprouts and sliced beef brisket thoroughly.
Slice the onion and green onion thinly.
Place the sliced beef brisket in a pan and stir-fry.
When the fat is rendered, add the onion and green onion and stir-fry together.
Add the soybean sprouts, cover the lid, and let them cook.
Mix together gochujang, soy sauce, minced garlic, red chili powder, and black pepper to make the seasoning sauce.
Add the sauce and mix everything evenly.
Lower the heat and cook for an additional 5 minutes.
Transfer the finished dish to a plate.