In a small bowl, mix 1 tbsp potato starch with 3 tbsp water to create your sauce thickener. Set aside.
Drizzle a bit of oil into a pan over medium heat. Add 200g of stir-fried beef and ¼ of the chopped onions. Let it cook slightly.
Stir in 1 tbsp ginger powder, 1 tbsp minced garlic, 1 tbsp soy sauce, and a pinch of MSG.
Add the remaining chopped onions and mix well.
Stir in 1.5 tbsp black bean paste (or adjust to your liking), then add 200ml of water. Turn off the heat and set the sauce aside.
While the sauce rests, cook your noodles according to package instructions. Drain and rinse well.
Return the sauce pan to the heat. Add ½ tbsp sugar, your prepared sauce thickener, and 1 tbsp oyster sauce. Stir to combine and let the sauce thicken slightly.
Plate the noodles and pour the luscious jjajang sauce over them.
Garnish with sliced cucumber, danmuji on the side, and a sprinkle of gochugaru for a final kick.
