Preheat your oven to 375°F (190°C) and lightly grease a small oven-safe baking dish.
In a large skillet over medium heat, add the olive oil and sauté the diced yellow onion and minced garlic until translucent and fragrant.
Add the fresh spinach to the skillet in batches, stirring until completely wilted. Remove from heat and let cool slightly.
Place the cooked spinach in a clean kitchen towel or fine-mesh strainer and squeeze out as much liquid as possible to prevent a soggy crust.
In a medium mixing bowl, whisk together the liquid egg whites, Greek yogurt, crumbled feta cheese, chopped dill, sea salt, black pepper, and nutmeg.
Stir the squeezed spinach into the egg mixture until well combined.
Lay one sheet of phyllo dough into the prepared baking dish, allowing the edges to hang over. Lightly brush or spray with a tiny amount of oil, then top with the second sheet.
Pour the spinach and egg filling into the center of the phyllo sheets.
Fold the overhanging edges of the phyllo dough back over the filling to create a rustic border.
Bake for 30-35 minutes, or until the egg filling is set and the phyllo crust is golden brown and crisp.
Allow the pie to cool for 5 minutes before slicing and serving.