Preheat your oven to 375°F (190°C).
Thaw the frozen spinach completely and place it in a clean kitchen towel, squeezing forcefully to remove every drop of excess moisture.
In a medium mixing bowl, whisk together the egg whites, Greek yogurt, crumbled feta, chopped green onions, dill, sea salt, black pepper, and nutmeg.
Stir the squeezed-dry spinach into the egg mixture until well combined.
Lightly brush a small oven-safe baking dish or ramekin with half of the olive oil.
Lay one sheet of phyllo dough into the dish, allowing the edges to hang over, brush lightly with the remaining oil, and top with the second sheet.
Pour the spinach and egg mixture into the center of the phyllo dough.
Fold the overhanging edges of the phyllo dough inward over the filling to create a rustic crust.
Bake for 30 to 35 minutes until the egg mixture is fully set in the center and the pastry is a deep golden brown.