Preheat your oven to 375°F and lightly grease a 9-inch pie dish with a small amount of oil.
Peel and thinly slice the sweet potato into rounds, then layer them across the bottom and up the sides of the dish to create a crust.
Bake the sweet potato crust for 10 minutes until slightly tender and set.
While the crust bakes, sauté the fresh spinach in a pan with olive oil until wilted, then squeeze out any excess moisture using a paper towel.
In a large mixing bowl, whisk together the eggs, egg whites, Greek yogurt, sea salt, black pepper, and garlic powder until smooth and creamy.
Arrange the sautéed spinach and crumbled feta cheese evenly over the pre-baked sweet potato crust.
Pour the egg mixture over the spinach and cheese, then sprinkle the top with fresh chives.
Bake for 25 to 30 minutes until the center is firm to the touch and the top is beautifully golden.