In a medium bowl, whisk together the whole egg, liquid egg whites, and Greek yogurt until the mixture is uniform and slightly frothy.
Heat the olive oil in a large non-stick skillet over medium heat, ensuring the surface is well-coated.
Add the baby spinach to the skillet and sauté for approximately 1 minute until the leaves are just wilted.
Pour the egg mixture into the skillet and let it sit undisturbed for about 30 seconds until the edges begin to set.
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, sea salt, and black pepper over the eggs while they are still slightly wet.
Continue to fold the eggs gently for another minute until they are cooked through but still appear moist.
Remove the skillet from the heat immediately and garnish the scramble with chopped fresh chives before serving hot.