Stir the saffron strands into the stock and set aside to infuse while you prepare the rest of the paella. Heat 1 tbsp oil in a paella pan or a large deep frying pan with a lid. Tip in the chorizo and fry for about 3 minutes until crisp and the oil has been released. Remove the chorizo and drain on kitchen paper, leaving the oil in the pan.
Stir the chicken into the pan and fry over a high heat for 7-8 minutes, or until the meat is golden and cooked through. Transfer the chicken to a bowl and set aside. Pour another 1 tbsp of oil into the pan, tip in the chopped onion and garlic and stir-fry for 4-5 minutes, until softened and just starting to colour. Stir in the pepper and paprika with the remaining tablespoon of oil and stir-fry for a further 1-2 minutes. The pan should have lots of crispy, brown bits on the bottom, which will all add flavour.
With the heat still quite high, quickly stir in the rice so it is well-coated in the oil, then pour in the saffron-infused stock plus 450ml boiling water, scraping up the sticky brown bits from the bottom of the pan with a wooden spoon. Return the browned chicken pieces to the pan, then add the chopped tomatoes. Cover the pan and cook on a medium heat for 10 minutes, stirring once or twice. Scatter the peas, prawns and fried chorizo over the top, cover again and leave to cook a further 5 minutes, or until the rice is just cooked and most of the liquid in the pan has been absorbed.
Remove the pan from the heat, put the lid on and leave to rest for 5 minutes. Stir a few times to mix the ingredients, season to taste and scatter over the chopped parsley. Serve with lemon wedges and an extra drizzle of oil, if you like.