Put your frying pan back on a low-heat (!). It will still have residual heat from the previous step.
Then add in 3 Tablespoons of cooking oil. Let it get hot.
Once hot, place the Chunjang paste (4 Tablespoons) into the oil. The paste will gently sizzle in the oil. (Adjust heat if necessary.) Then stir around in the oil for 2 minutes with a wooden spoon.
After 2 minutes, add in the stir-fried veggies into the frying pan. Mix and stir everything together for additional 2 minutes.
Now, add in water (1 cup). Raise the heat to a medium and bring the mixture up to a gentle boil.
Add in sugar (1T) and oyster sauce (1T).
Let the mixture gently boil until the potatoes/zucchini gets soft. Stir occasionally. It should take around 5 minutes.
In the meanwhile, let's make starch water: Mix water (3T) and corn starch (3T)
Add in about half of the starch water to thicken the sauce. (Note: When you add the starch water, pour in a circular motion. You don't want it to pour in just one area.) Check the consistency and add more starch water if needed.
Turn off the heat. Grab some rice and place it on a large plate.