Preheat your oven to 375°F and lightly grease a small oven-safe baking dish with a drop of olive oil.
Place the thawed spinach in a clean kitchen towel and squeeze forcefully until all excess liquid is removed and the spinach is very dry.
In a mixing bowl, whisk together the egg whites, whole egg, and Greek yogurt until smooth and well combined.
Fold in the dried spinach, crumbled feta, sliced scallions, minced garlic, fresh dill, sea salt, black pepper, and nutmeg.
Lay the phyllo dough sheets into the prepared dish, allowing the edges to hang over the sides, and lightly brush the edges with the remaining olive oil.
Pour the spinach and egg mixture into the center, fold the overhanging phyllo edges back over the filling, and bake for 30 to 35 minutes until the pastry is golden and the center is firm.