Preheat the oven to 375 degrees F. Lightly grease an 8 x 8 inch or 9-inch round baking dish with olive oil. I like to line the dish with parchment paper to make it easier to transfer out of the dish and cut on a cutting board.
If you are using fresh spinach, heat a large pan (I used a 13” pan) over medium heat. If you’re using frozen spinach, you can use a 10” skillet because you won’t need to cook the spinach. Add fresh spinach and a couple tablespoons water and cook until wilted. Transfer mixture to a colander or nut milk bag and strain the spinach to remove the excess liquid. Be careful because the mixture will be hot. Use gloves or allow the mixture to cool down a bit before pressing. I like to press it in a colander with a wooden spoon and I use the same spoon to break up the spinach. If using frozen, defrosted spinach, you will need to press the excess liquid before using it.
To the same skillet, add the oil and scallions and saute until softened, about 1 to 2 minutes.
In a large bowl, whisk together the flour, baking powder, and salt. Add the milk, eggs, and melted butter and whisk until it forms a batter. Stir in the pressed spinach and sauteed scallions, dill, mozzarella, and feta cheese until fully incorporated. Pour the batter into the prepared baking dish and smooth the top with a spatula. Sprinkle parmesan cheese over the top.
Bake for 40-45 minutes, until golden brown on the top and it springs back when you press your fingers over the center of the pie. Remove from the oven and allow to cool for 15-20 minutes before cutting. It will cut much more easily if you allow it to cool.