Preheat the oven to 350 degrees F and lightly spray a large (13” x 9”) casserole dish or baking dish with cooking spray.

Heat the avocado oil over medium-high heat in a large nonstick skillet. After allowing the skillet to warm up for a minute or two, add the onion and sauté it for about 8 minutes, until it is golden-brown.

Add the mushrooms and sea salt, stir well, and cover the skillet. Allow the mushrooms to cook, stirring occasionally, until they turn brown and much liquid has leached out, about 8 minutes.

Remove the lid and stir in the garlic, followed by the ground breakfast sausage. Use a spatula to break up the ground turkey and continue cooking, stirring constantly, until the turkey is cooked through, about 5 to 8 minutes.

Add the baby spinach to the skillet, cover, and allow it to cook until the spinach has wilted, about 2 to 3 minutes. 

Stir the turkey and mushroom mixture well, then transfer it to the casserole dish, spreading it into an even layer. Sprinkle the feta cheese over everything.

Crack the eggs into a large bowl and beat them until very well combined.

Pour the egg mixture over the meat mixture evenly. If need be, you can stir everything around a bit to ensure the ingredients are evenly distributed.

Bake on the center rack of the preheated oven for 40 to 50 minutes, or until the casserole has set up in the center and has cooked through.

Allow the casserole to cool for 20 minutes before slicing into individual pieces and serving (this will allow for cleaner slices). Serve it with a dollop of sour cream or yogurt, hot sauce, crispy bacon, and chopped green onions for a lovely holiday breakfast.