Put a large 12-inch skillet with a lid over medium-high heat and add the oil.

Add the smoked sausage to the skillet in one layer. Cook for 4 to 5 minutes, turning once or twice, until the slices are browned in spots.

Transfer the sausage to a plate and leave the fat in the skillet.

Put the halved potatoes into the same skillet, cut side down, and sprinkle them with 1/2 teaspoon of the salt.

Pour 1/2 cup water into the skillet and cover with the lid.

Cook the potatoes for 6 to 8 minutes, until they are almost tender when pierced with the tip of a knife.

Remove the lid and keep cooking for 3 to 4 minutes, turning the potatoes once, until the water cooks away and the cut sides start to turn golden.

Add the sliced onion and the white parts of the scallions to the skillet.

Cook for 3 minutes, stirring now and then, until the onion softens.

Add the garlic and ginger to the skillet. Cook for 30 seconds, stirring, until they smell fragrant.

Add the napa cabbage to the skillet a few handfuls at a time. Stir after each addition so it starts to wilt and fit in the pan.

Stir the soy sauce, rice vinegar, brown sugar, and remaining 1/4 teaspoon salt together in a small bowl.