Heat the oven to 375°F and coat a 2-quart baking dish with cooking spray.

Add the potatoes to a saucepan, cover with cold water, and season with half the salt. Bring to a boil and cook for 7 minutes, until the edges are tender but the centers remain firm.

Drain the potatoes thoroughly and let them steam-dry in the colander for 2 minutes.

Heat 1 teaspoon olive oil in a large nonstick skillet over medium-high heat. Brown the kielbasa for 3 to 4 minutes, turning once, then transfer it to a plate.

Reduce the heat to medium. Add the remaining oil and onion, then cook for 3 minutes until softened.

Whisk the milk and cornstarch together. Pour the mixture into the skillet and add the remaining salt, pepper, garlic powder, and smoked paprika. Simmer for 2 to 3 minutes, whisking, until the sauce coats a spoon.

Remove the skillet from the heat. Stir in the cheddar until melted, followed by the Greek yogurt and Dijon. Fold in the potatoes and kielbasa, then transfer everything to the baking dish.

Bake for 25 minutes, until the sauce bubbles around the edges and the potatoes are fork-tender. Rest for 10 minutes before serving.