Start by preparing the crust. Place the flour, polenta, salt, chipotle chilli flakes and oregano into your food processor and pulse briefly to mix. Add the butter to the processor and pulse until the butter resembles small peas in the flour. Pour in 4 tablespoons of ice cold water and continue to pulse until a ball of dough forms, adding a little more water if necessary. Tip the dough out onto a floured surface and pat gently to form a disc. Wrap in cling film and refrigerate for 30 minutes.
In a small bowl, mix together the ricotta, fresh oregano, garlic and oil until well combined. Season with salt and pepper.
Once the dough has chilled, remove from the fridge and roll out on a floured surface so that it's about 1/8" thick. Transfer the rolled out dough to a baking tray lined with parchment paper.
Spread the ricotta mixture over the crust, leaving a border a couple of inches wide around the edges. Lay the courgette slices in a concentric circle pattern on top of the ricotta. Brush the courgettes with a little oil and sprinkle with salt and pepper.
Preheat the oven to 180°C/350°F (fan) or hotter for conventional (190°C/375°F).
Brush the edges of the dough with the beaten egg and place in the fridge for 15-20 minutes to rest before baking.
Bake for 45 minutes or until golden brown. Allow to cool a little before slicing.
Fold the edges of the dough over the filling