Preheat your oven to 375°F (190°C).
Thaw the frozen spinach and squeeze it thoroughly in a clean kitchen towel until all excess moisture is removed and the spinach is very dry.
In a medium mixing bowl, whisk together the whole egg, liquid egg whites, and non-fat Greek yogurt until smooth.
Stir in the crumbled feta cheese, minced garlic, dried oregano, sea salt, and black pepper.
Fold the dried spinach into the egg mixture until it is evenly distributed.
Lightly brush a small oven-safe baking dish or skillet with a small amount of the olive oil.
Lay one sheet of phyllo dough into the dish, allowing the edges to hang over the sides, and brush very lightly with olive oil.
Place the second sheet of phyllo on top, rotating it slightly to cover different angles of the dish.
Pour the spinach and egg mixture into the center of the phyllo sheets.
Fold the overhanging edges of the phyllo dough back over the filling to create a rustic, open-faced crust.
Bake for 30 to 35 minutes until the filling is set and the phyllo is golden brown and flaky.