Preheat your oven to 375°F (190°C) and lightly grease a small oven-safe baking dish with a touch of olive oil.
In a skillet over medium heat, add the olive oil and the ground turkey sausage, breaking it up with a spatula until browned and cooked through.
Add the diced yellow onion and red bell pepper to the skillet, sautéing for 3-4 minutes until the vegetables are tender and fragrant.
Stir in the fresh spinach and cook just until wilted, then remove the skillet from the heat.
In a medium mixing bowl, whisk together the eggs, egg whites, nutritional yeast, sea salt, black pepper, and garlic powder until well combined and slightly frothy.
Transfer the sausage and vegetable mixture into the prepared baking dish, spreading it out into an even layer.
Pour the egg mixture over the top, ensuring it settles into all the crevices of the meat and vegetables.
Bake for 20-25 minutes, or until the center is set and the edges are lightly golden brown.
Let the casserole rest for 5 minutes before slicing and serving warm.