Preheat your oven to 375°F (190°C) and lightly grease a small oven-safe baking dish.
Heat the olive oil in a skillet over medium heat. Add the diced yellow onion and red bell pepper, sautéing for 3-4 minutes until the vegetables begin to soften.
Add the ground turkey sausage to the skillet, breaking it up with a spatula. Cook until the sausage is browned and fully cooked through.
Stir in the 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 large eggs, egg whites, sea salt, black pepper, and dried oregano until well combined.
Transfer the cooked sausage and vegetable mixture into the prepared baking dish, spreading it into an even layer.
Pour the egg mixture over the sausage and vegetables, ensuring everything is evenly submerged.
Bake for 20-25 minutes, or until the eggs are set in the center and the edges are lightly golden brown.
Allow the bake to cool for 5 minutes before slicing and serving.