Preheat your oven to 375°F.
Heat the olive oil in a 10-inch oven-safe non-stick skillet over medium heat.
Add the ground turkey and diced red onion to the skillet, breaking up the meat with a spatula until browned and cooked through.
Add the baby spinach to the pan and sauté for 1-2 minutes until just wilted.
In a medium bowl, whisk together the egg whites, sea salt, black pepper, and garlic powder until slightly frothy.
Pour the egg white mixture into the skillet, ensuring it evenly covers the turkey and vegetables.
Sprinkle the crumbled feta cheese over the top of the egg whites.
Place the skillet in the oven and bake for 12 to 15 minutes, or until the frittata is set in the center and the edges are lightly golden.
Remove from the oven, let cool for 2 minutes, and slice into wedges to serve.