Preheat oven to 375°F (190°C) and lightly grease a small oven-safe baking dish.
Place the thawed spinach in a clean kitchen towel and squeeze firmly until all excess moisture is removed.
In a medium bowl, whisk together the egg whites, whole egg, Greek yogurt, sea salt, black pepper, and nutmeg.
Stir the squeezed spinach, crumbled feta, chopped dill, and sliced scallions into the egg mixture until well combined.
Lay one sheet of phyllo dough on a clean surface, brush lightly with olive oil, and fold it to fit the bottom and sides of the baking dish.
Repeat with the second sheet of phyllo, rotating it slightly to ensure the dish is well-covered.
Pour the spinach and egg mixture into the phyllo-lined dish and gently fold any overhanging pastry edges toward the center.
Bake for 30 to 35 minutes until the filling is set and the phyllo crust is golden brown and flaky.