Preheat your oven to 375°F and lightly brush a small oven-safe baking dish with the olive oil.
Place the cooked spinach in a clean kitchen towel and squeeze firmly until all excess moisture is removed and the spinach is very dry.
In a medium mixing bowl, whisk together the large egg, liquid egg whites, and nonfat Greek yogurt until smooth.
Fold in the dried spinach, crumbled feta cheese, chopped dill, sliced green onions, garlic powder, sea salt, and black pepper.
Lay one sheet of phyllo dough into the baking dish, allowing the edges to hang over the sides, and repeat with the remaining two sheets.
Pour the high-protein spinach and egg mixture into the center of the phyllo-lined dish.
Gently fold the overhanging edges of the phyllo dough over the top of the filling to create a rustic border.
Bake for 30 to 35 minutes until the egg filling is completely set and the phyllo pastry is deeply golden and crisp.
Allow the pie to cool for 5 minutes before slicing and serving.