In a medium bowl, mix onion, spinach, dill, parsley and cheeses and pour into the pie dish. Use a spoon to spread mixture to cover the bottom of the dish.
Sift the flour and baking powder in a medium bowl. Add the milk, oil, eggs, salt and pepper and mix well. Pour the mixture into the pie dish.
Bake pie for 25 minutes or until lightly brown on top and knife comes out clean from the center. Let stand at least 5 minutes before serving. Serve hot or room-temperature.