Dice the onion, pork, potato, and carrot.
Heat cooking oil in a pan and stir-fry the pork.
Add the onion, potato, and carrot, and stir-fry together.
Add the chunjang (black bean paste) and stir well with the ingredients.
Add water, sugar, soy sauce, and pepper, and bring to a boil.
Adjust the thickness with starch water.
Pour the jajang sauce over rice to serve.