Preheat your oven to 375°F and lightly grease a small oven-safe baking dish with a touch of oil.
Clean the leeks thoroughly, then thinly slice them along with the Yukon gold potato; dice the chicken breast into small, uniform bite-sized pieces.
Heat the olive oil in a skillet over medium heat and sauté the leeks for 3-4 minutes until they are softened and fragrant.
In a small mixing bowl, whisk together the Greek yogurt, egg, sea salt, black pepper, and garlic powder until the mixture is smooth and creamy.
Arrange half of the potato slices in the bottom of the baking dish, then layer the diced chicken and sautéed leeks on top.
Place the remaining potato slices over the chicken layer and pour the yogurt mixture evenly over the entire dish.
Sprinkle the parmesan cheese over the top, cover the dish with foil, and bake for 25 minutes.
Remove the foil and bake for an additional 15 minutes, or until the potatoes are tender and the cheese is beautifully golden brown.