Step 1Heat the grape seed oil in a wok or large skillet over medium-high heat. Add the pork and potato and cook, stirring occasionally, until the pork is golden brown and crisp, 4 to 5 minutes.
Step 2Add the onion and zucchini and cook, stirring, until the onion starts to look translucent, 3 to 4 minutes. Add the black bean sauce and cook, stirring, for 1 minute. Stir in 2 cups water, raise the heat to high and bring to a boil. Cover partially with a lid, reduce the heat to medium-low and simmer until the pork and potato are cooked through, about 10 minutes.
Step 3Meanwhile, cook the noodles according to the package’s directions.
Step 4Uncover and smash a few potatoes into the sauce to thicken it. Add the sugar and sesame oil and stir well. Transfer the noodles to a serving dish and top with the sauce and cucumber.
Vegan jajangmyeon: Substitute 8 ounces thick shiitake mushrooms, stemmed and cut into ½-inch dice, for the pork belly, and sear them in 3 tablespoons oil in a hot skillet; proceed as above.