Position rack in centre of oven and preheat to 205°C (185°C fan-forced). Line a large rimless baking tray (or turn a rimmed tray upside down) with baking paper.
In a large frying pan over medium heat, bring ¼ cup (60ml) water to a simmer. Working in batches, add the spinach, then cover and steam for 3 mins or until spinach wilts. Transfer to a baking tray to cool.
Place spinach in a clean tea towel. Squeeze out as much water as possible. Finely chop spinach and transfer to a medium bowl with ¼ cup each of the spring onion, basil, dill, mint, parsley and oregano. Add fetta, two-thirds of the garlic and half the lemon rind. Stir to combine. Season with salt and pepper.
On a lightly floured surface, roll out each pastry sheet to a 30cm square. Using a small sharp knife, cut each sheet into a 30cm disc. Place 1 disc on the lined tray.
Brush a little egg along the edge of the pastry disc on the tray. Spread the spinach mixture over the pastry, leaving a 1cm border. Top with the second pastry disc and gently press along the edge to seal.
Using a 5cm-wide glass, make an indent in the centre of the tart. Freeze for 15 mins or until firm enough to handle. Using a small sharp knife, cut the tart into quarters, stopping when you reach the centre circle. Cut each quarter into 4 pieces to make 16 pieces.
Gently pull each piece away from the centre and twist 3 times to lengthen slightly and expose the filling. Freeze for 10 mins. Brush the tart all over with egg. Bake for 35 mins or until golden.
Meanwhile, in a small bowl, combine the yoghurt, lemon juice and remaining spring onion, basil, dill, mint, parsley, oregano, garlic and lemon rind. Season with salt and pepper.
Transfer the tart to a serving platter. Serve warm or at room temperature with the lemony yoghurt.
Tip: [\SERVE WITH... basil leaves, lemon zest and olive oil\,\SWAP ME... To save time, swap the babyspinach leaves for 500g frozen chopped spinach, thawed, excess liquid removed.\]