Preheat your oven to 375°F (190°C).
In a non-stick skillet, sauté the fresh spinach over medium heat until fully wilted, then transfer to a colander and squeeze out all excess liquid.
In a medium mixing bowl, whisk together the liquid egg whites, whole egg, and nonfat Greek yogurt until smooth.
Stir in the wilted spinach, crumbled feta cheese, sea salt, black pepper, garlic powder, and chopped fresh dill.
Lightly brush a small oven-safe baking dish with a portion of the olive oil.
Layer the phyllo dough sheets into the dish, allowing the edges to hang over the sides, and brush lightly with the remaining olive oil.
Pour the spinach and egg mixture into the center of the phyllo dough layers.
Fold the overhanging edges of the phyllo dough back over the top of the filling to create a rustic border.
Bake for 25 to 30 minutes, or until the filling is set and the pastry is a deep golden brown.