In a medium mixing bowl, whisk together the whole eggs, egg whites, Greek yogurt, sea salt, black pepper, and garlic powder until the mixture is completely smooth and aerated.
Place a medium non-stick skillet over medium heat and add the ghee, swirling to coat the bottom of the pan.
Add the finely diced red onion to the skillet and sauté for 2 to 3 minutes until softened and translucent.
Add the fresh baby spinach to the pan and toss with the onions until the leaves are just wilted, which should take about 1 minute.
Lower the heat to medium-low and pour the egg mixture into the skillet, allowing it to sit undisturbed for 30 seconds to begin setting.
Using a silicone spatula, gently push the eggs from the outer edges toward the center to create large, soft curds.
Sprinkle the crumbled feta cheese over the eggs while they are still slightly wet.
Continue to fold the eggs gently for another 1 to 2 minutes, then remove the pan from the heat while the eggs still look slightly moist to ensure a creamy finish.