Preheat the oven to 190 °C (fan-forced).
Slice the leek and sauté in a couple of tablespoons of olive oil over gentle heat for 3 minutes until gently caramelised.
In a large bowl, combine the spinach, spring onions, sautéed leek, dill, parsley, salt, and pepper. Squeeze gently and mix until the greens soften slightly. Add the feta, stir through until combined and set aside.
While the greens cool slightly, generously grease a 20 × 30 cm baking pan or 30cm round baking tray with plenty of olive oil. Sprinkle 1 tablespoon white cornmeal evenly over the base.
In a separate bowl, whisk together Greek yoghurt, olive oil, eggs, and water until smooth. Add gluten-free flour, white cornmeal, sea salt, and baking soda. Whisk until a smooth, slightly runny batter forms. Adjust water slightly if needed to maintain pourable consistency or increase gf flour if too thin.
Pour ⅔ of the batter into the prepared pan and spread evenly. Spoon the filling evenly over the batter. Pour the remaining batter over the filling, allowing some of the greens and feta to peek through. Sprinkle with sesame seeds.
Bake for 45-50 minutes, or until the top is golden and set. Loosely cover with foil if the top browns too quickly.
Allow to rest for 20–30 minutes before cutting into squares. Serve slightly warm or at room temperature.
