Preheat your oven to 375°F and lightly grease a small oven-safe baking dish with a touch of olive oil.
Thaw the frozen spinach completely and use a clean kitchen towel to squeeze out every drop of excess liquid.
In a medium mixing bowl, whisk together the liquid egg whites and the whole egg until well combined.
Fold in the squeezed spinach, crumbled feta cheese, chopped green onions, and minced garlic.
Season the mixture with dried dill, sea salt, and black pepper, stirring until the ingredients are evenly distributed.
Lay one sheet of phyllo dough into the prepared baking dish, allowing the edges to hang over, and lightly brush with olive oil.
Place the second sheet of phyllo dough on top, rotating it slightly to cover more surface area.
Pour the spinach and egg mixture into the center of the phyllo-lined dish.
Gently fold the overhanging edges of the phyllo dough back toward the center to create a rustic crust.
Bake for 25 to 30 minutes until the egg filling is firm and the phyllo is golden brown and flaky.