Grate the potatoes and place them in a bowl of cold water with a pinch of salt for 15 minutes to remove excess starch.

While the potatoes are soaking, heat 2 tablespoons of olive oil in a skillet over medium heat. Sauté the green onion until softened.

Add the spinach to the skillet, seasoning with salt and pepper. Cook until wilted.

Stir in the sliced mushrooms, then season with salt, pepper, and oregano. Add the minced garlic and cook until the mushrooms are golden and their liquid evaporates. Set the mixture aside to cool.

Drain the soaked potatoes and squeeze out any excess water. In a large bowl, mix the drained potatoes with mozzarella, eggs, chopped parsley, salt, pepper, and oregano.

Preheat the oven to 200°C (390°F) and grease a round baking dish. Press the potato mixture into the dish to form a crust.

Bake the crust in the preheated oven for 35-40 minutes until golden brown.

Once baked, spoon the cooled spinach and mushroom mixture into the potato crust. Top with the remaining mozzarella and torn mozzarella fior di latte.

Return the pie to the oven for an additional 10-15 minutes, until the cheese is melted and bubbly.

Let the pie cool for 5 minutes before serving. Garnish with extra Parmesan and fresh parsley.