Preheat your oven to 375°F and lightly grease a 9x13-inch baking dish with a small amount of olive oil.
Heat the olive oil in a large skillet over medium heat, then add the diced yellow onion and minced garlic, sautéing until fragrant and translucent.
Add the ground turkey sausage to the skillet, breaking it into small crumbles with a spatula, and cook until completely browned and no longer pink.
Stir in the fresh baby spinach and cook for 1-2 minutes until just wilted, then remove the skillet from the heat to let the mixture cool slightly.
In a large mixing bowl, whisk together the eggs, liquid egg whites, and Greek yogurt until the mixture is smooth and well combined.
Whisk in the sea salt, black pepper, and dried oregano to ensure the seasonings are evenly distributed throughout the egg base.
Spread the cooked sausage and spinach mixture evenly across the bottom of the prepared baking dish.
Pour the egg and yogurt mixture over the sausage and spinach, then sprinkle the crumbled feta cheese evenly over the top.
Bake for 35-40 minutes until the eggs are set in the center and the top is lightly golden brown.
Allow the bake to cool for 10 minutes before slicing into 9 even portions for easy meal prep throughout the week.