Preheat your oven to 350°F and lightly grease six wells of a standard muffin tin with a small amount of the olive oil.
Heat a non-stick skillet over medium heat with the remaining olive oil and brown the ground turkey until fully cooked and no longer pink.
Add the fresh spinach to the skillet and sauté for 1-2 minutes until just wilted, then remove the pan from the heat to cool slightly.
In a medium mixing bowl, whisk together the large eggs, liquid egg whites, sea salt, black pepper, red pepper flakes, and lemon zest until well combined.
Divide the cooked turkey and spinach mixture evenly among the six prepared muffin cups.
Pour the egg mixture over the turkey and spinach in each cup, filling them about three-quarters of the way to the top.
Sprinkle the crumbled feta cheese evenly over the top of each egg cup.
Bake for 20 to 25 minutes, or until the eggs are set in the center and the tops are beginning to turn a light golden brown.