An hour or two before you start cooking, rinse the lentils well and then leave them in warm water to soak.
Warm the oil in a large saucepan over a low heat, then add the onion, garlic and oregano and fry until soft.
Drain and rinse the lentils and add to the pan.
Stir in the stock and turn up the heat. As soon as it boils, turn down to a simmer, cover and leave for 10 minutes – the lentils should absorb all of the liquor and turn soft and pale.
Take off the heat, stir in the grated cheese, season to taste.
Once the mixture has cooled a little, stir in one beaten egg then leave to cool completely.To make the pastry
Put the flour, cornmeal and cold, cubed butter into a bowl and rub into a crumb.
Add ¾ of the beaten eggs (keeping ¼ back for later) and cut into the crumb with a round knife.
Add the water a little a time until you can press the mix together to get a manageable dough.
Bring together and knead into smooth ball, wrap in clingfilm and put in the fridge for 15 minutes.To assemble
Preheat the oven to 200C/390F (180C/355F fan). Grab your chilled pastry and cut off one third, which you can rewrap. Roll the larger piece of dough out on a floured surface and until your disc is about 30cm wide.
Line a 23 cm nonstick quiche tin with the pastry and set aside, leaving the overhang untrimmed.
Tip the cooled lentil filling into the pastry-lined dish and brush the exposed pastry edges with water.
Roll out the remaining pastry to form a disc just a couple of centimetres wider than you tip and place on top.
Press the edges with a fork to seal, then trim away any excess pastry.
Brush the top with the beaten egg you reserved earlier, then make a couple of slits in the centre with the end of a sharp knife.
Bake for 40 minutes until golden brown and cooked through.
Allow to cool a little before cutting into slices. Enjoy!