First preheat your oven to 220ºC/425ºF/gas 7, then place your potatoes with 2 of your lemons into a small pan of water and boil for 5 minutes. Drain, and then prick the lemons all over with a knife. (The reason for doing this is that you are going to put them inside the chicken and their wonderful juices will be released while cooking. They will burst with flavour and fragrance, and the heat from the lemons will help the chicken to cook quicker from the inside as well as making it taste and smell amazing.) Remove the parsley leaves from the stalks and put to one side. Stuff the chicken with your hot lemons and the parsley stalks. Then season the chicken and the potatoes with a tiny pinch of salt and freshly ground black pepper, and slice your chorizo at an angle, 0.5cm/¼ inch thick.
Get yourself an appropriately sized baking tray. Take a piece of greaseproof paper and wet it under a tap so it becomes flexible, then shake it out and lay it into the baking tray. Place the potatoes into the centre of the greaseproof paper, then place the chicken on top and sprinkle with the chorizo and a little of your chopped parsley. Drizzle with a little olive oil. Cook in the preheated oven for around 1 hour 20 minutes.
While the chicken and potatoes are cooking you can make what the Italians call gremolata, by finely chopping the zest of your 2 remaining lemons and mixing it with the chopped parsley and garlic. Season with a little pinch of salt and freshly ground black pepper and toss together to create a really fragrant seasoning-type garnish. Remove the tray from the oven, take the chicken out and put to one side to rest. Give the potatoes a shake about and put them back in the oven for a few minutes to crisp up.
Carve the chicken and divide between 8 plates, with the potatoes. The potatoes will have taken on the smoky paprika flavour from the chorizo, so if there is any juice left over in the tray, pour every last drop over the plates. When you sprinkle over the gremolata it will hit the hot juice and smell fantastic. You're going to love this one! A rocket salad goes really well with it.