Cut vegetables such as onion, carrot, potato, zucchini, and bell pepper into bite-size pieces.
Heat cooking oil in a pan and stir-fry the vegetables over medium heat.
When the vegetables are about halfway cooked, add minced garlic and stir-fry together.
Add chunjang (black bean sauce) and stir-fry evenly to mix well.
Add water and potato starch to adjust the thickness of the sauce.
Season with salt and pepper, then turn off the heat.
Serve the sauce over rice.