Preheat your oven to 375°F (190°C) and lightly grease a small baking dish with a touch of ghee or avocado oil.
In a skillet over medium heat, melt 1 tsp of ghee and sauté the finely diced yellow onion until translucent and fragrant.
Add the fresh spinach to the skillet and cook for 1-2 minutes until just wilted, then remove from heat to cool slightly.
In a medium mixing bowl, whisk together the large eggs, liquid egg whites, sea salt, black pepper, and garlic powder until well combined.
Spread the sautéed onion and spinach evenly across the bottom of the prepared baking dish.
Pour the egg mixture over the vegetables and sprinkle the crumbled feta cheese evenly across the top.
Bake for 20-25 minutes, or until the eggs are set in the center and the edges are slightly puffed and golden.
Allow the bake to cool for 5 minutes before slicing and serving warm.