Set a large 12-inch skillet with a lid over medium heat.

Add the olive oil to the skillet and heat it for about 30 seconds, until it looks thin and moves easily across the pan.

Add the sliced kielbasa to the skillet in a mostly even layer.

Cook the kielbasa for 2 to 3 minutes, until the bottom sides have browned spots.

Stir the kielbasa and cook for 2 more minutes, until more sides are lightly browned.

Transfer the kielbasa to a plate, leaving the fat in the skillet.

Add the potatoes to the skillet.

Sprinkle the potatoes with 1/2 teaspoon of the salt and 1/4 teaspoon of the black pepper.

Spread the potatoes into an even layer and cook them for 4 minutes without stirring, until the bottoms start to turn golden.

Stir the potatoes and cook for 3 minutes more, until several sides have color.

Add the sliced onion to the skillet with the potatoes.

Cook the onion for 2 minutes, stirring often, until it starts to soften.