Preheat your oven to 375°F and lightly grease a small oven-safe baking dish.
Place the fresh spinach and sliced scallions in a skillet over medium heat, cooking until completely wilted.
Transfer the spinach to a clean kitchen towel and squeeze firmly to remove every drop of excess moisture.
In a medium bowl, whisk together the liquid egg whites, whole egg, Greek yogurt, sea salt, black pepper, and garlic powder until smooth.
Stir the squeezed spinach, crumbled feta cheese, and chopped fresh dill into the egg mixture.
Lay one sheet of phyllo dough into the baking dish, brush lightly with olive oil, and top with the second sheet.
Pour the spinach and egg custard over the phyllo sheets, then fold the overhanging edges of the pastry toward the center.
Bake for 30 to 35 minutes until the filling is set and the phyllo is deeply golden and flaky.