Prepare the Ingredients: In a large bowl, combine the chopped spinach, crumbled feta, grated cheddar cheese (reserve a large handful for later), milk, gluten-free flours, fresh herbs, whisked eggs, green onions, olive oil, salt, and pepper. Mix thoroughly to ensure the cheese and herbs are evenly distributed among the spinach.
Preheat the Oven and Prepare the Bakeware: Preheat the oven to 180°C fan-forced / 200°C conventional (400°F). Line a 30cm x 20cm baking dish with baking paper, or, if using a non-stick tray, brush it generously with olive oil.
Assemble the Pie: Pour the spinach and feta mixture into the prepared baking dish and flatten it evenly with the back of a spoon. Sprinkle the reserved cheddar cheese evenly over the top - add more if needed.
Bake: Bake for 50-55 minutes, rotating the dish halfway through to ensure even cooking. The top should be golden, and the filling should be set.
Cool and Serve: Let the pie cool in the baking dish for a minimum of 30 minutes. If needed, transfer it to a wire rack to cool further. Slice into squares and serve.
