Preheat oven to 375°F and lightly grease a small oven-safe baking dish.
Squeeze all excess moisture from the thawed spinach using a clean kitchen towel until very dry.
In a medium bowl, whisk together egg whites, whole egg, Greek yogurt, sea salt, black pepper, and garlic powder until smooth.
Stir in the dried spinach, crumbled feta, sliced green onions, and chopped fresh dill.
Lay one phyllo sheet into the dish, brush lightly with olive oil, and top with the second sheet.
Pour the egg and spinach mixture into the center of the phyllo sheets.
Fold the overhanging phyllo edges inward toward the center to create a rustic border.
Bake for 28 minutes until the eggs are set and the pastry is golden brown.
Allow the pie to rest for 5 minutes before cutting into wedges and serving.