Prepare the Spinach: Wash the spinach thoroughly and set aside.
Sauté Aromatics: In a large pan, heat the olive oil over medium heat. Add the chopped onion and minced garlic. Sauté until the onion becomes soft and translucent, about 5 minutes.
Prepare Egg Mixture: In a mixing bowl, whisk together the eggs, milk, and flour until smooth. Season with salt, pepper, and chili flakes if using.
Cook Spinach: Add the spinach to the pan with the sautéed onions and garlic. Stir until the spinach wilts down, which should take a couple of minutes.
Add Feta and Parsley: Once the spinach is wilted, stir in the crumbled feta cheese and chopped fresh parsley. Mix well to combine.
Combine with Egg Mixture: Pour the egg mixture over the spinach and feta in the pan. Stir gently to ensure everything is evenly distributed.
Transfer to Baking Dish: Preheat your oven to 180°C (356°F). Transfer the mixture to a greased baking dish. Sprinkle the grated mozzarella cheese evenly over the top.
Bake: Place the baking dish in the preheated oven and bake for 25 to 30 minutes, or until the top is golden brown and the bake is set.
Serve: Remove from the oven and let it cool slightly before serving. Enjoy your meal!