Heat the oven to 180C/fan 160C/gas 4. Heat a frying pan, add the chorizo and cook over a medium heat, until crisp. Turn the heat to low and add the onion and garlic, frying gently for 10 minutes. Put the spinach in a colander and pour over a kettle of water. Once cooled, squeeze as much water out as possible, roughly chop and stir through the chorizo with the oregano and manchego. Bring a pan of salted water to the boil and blanch the potato for 4-5 minutes until tender. Drain and add to the mix and allow to cool.