Preheat your oven to 375°F (190°C).
Thaw the frozen spinach and place it in a clean kitchen towel, squeezing forcefully until all excess moisture is removed.
In a large mixing bowl, whisk together the egg, egg whites, and Greek yogurt until the mixture is smooth and well-combined.
Fold in the squeezed spinach, crumbled feta cheese, sliced green onions, chopped dill, minced garlic, sea salt, and black pepper.
Lightly grease a small oven-safe baking dish with a tiny drop of olive oil.
Pour the spinach and egg mixture into the prepared baking dish, spreading it into an even layer.
Take the two sheets of phyllo dough and lightly brush or mist them with the remaining olive oil.
Gently crinkle the phyllo sheets and place them on top of the spinach mixture to create a textured, ruffled crust.
Bake for 30 to 35 minutes, or until the filling is firm and the phyllo topping has turned a deep golden brown.