For the chicken, preheat the oven to 200C/400F/Gas 6.
Using a knife, make a deep cut in the side of each chicken breast to create a pocket. Season each chicken breast, to taste, with salt and freshly ground black pepper.
Heat one tablespoon of the olive oil in a frying pan over a medium heat, add the shallot and fry for 1-2 minutes, or until just softened. Remove from the heat.
In a bowl, mix together the shallot, chorizo, parsley and lemon zest until well combined. Season, to taste, with freshly ground black pepper.
Fill each chicken breast with the chorizo mixture.
Heat the remaining olive oil in a separate, ovenproof frying pan over a high heat, add the stuffed chicken breasts and fry for 1-2 minutes on each side, or until golden-brown on both sides.
Transfer to the oven and cook for 15-18 minutes, or until completely cooked through. (The chicken is cooked through when the juices run clear when pierced in the thickest part with a skewer.) Remove the chicken breasts from the pan and set aside on a warm plate to rest.
Meanwhile, for the sautéed chorizo and potatoes, heat a separate frying pan over a medium heat, add the chorizo and fry for 2-3 minutes, or until the oil comes out of the chorizo.
Add the potatoes, and fry for 3-4 minutes, or until crisp and golden-brown.
Add the tomatoes and fry for a further 2-3 minutes, or until just softened.
Add the parsley, then season, to taste, with salt and freshly ground black pepper and stir well to combine.
For the spinach, heat the butter in a separate frying pan over a medium heat until melted, add the spinach and fry for 1-2 minutes, or until just wilted. Season, to taste, with salt and freshly ground black pepper.
To serve, divide the spinach equally among four serving plates. Carve the chicken diagonally into three pieces and arrange the pieces on top of the spinach. Spoon the sautéed chorizo and potatoes alongside. Drizzle over any remaining juices from the chorizo.