Preheat your oven to 375°F (190°C) and lightly grease a small oven-safe baking dish.
In a non-stick skillet over medium heat, add the olive oil and sauté the diced yellow onion until translucent, about 3 minutes.
Add the ground turkey sausage to the skillet, breaking it apart with a spatula, and cook until browned and fully cooked through.
Stir in the fresh baby spinach and cook for 1 minute until just wilted, then remove the skillet from the heat.
In a medium mixing bowl, whisk together the whole eggs, liquid egg whites, sea salt, black pepper, and garlic powder until well combined.
Transfer the sausage and spinach mixture into the prepared baking dish, spreading it out into an even layer.
Pour the egg mixture over the sausage and vegetables, ensuring everything is submerged.
Bake for 20-25 minutes, or until the eggs are set in the center and the top is lightly golden.
Allow the bake to cool for 5 minutes before slicing and serving.