Cut the onion and pork into bite-sized pieces.
Heat cooking oil in a pan and stir-fry the pork.
Add onion, zucchini, and potato and stir-fry together.
Add black bean paste (chunjang) and sugar, then stir-fry.
Add water and cornstarch slurry, then simmer until thickened.
Pour the finished jajang sauce over rice.