Heat half the oil in a large paella, sauté or frying pan and gently fry the chorizo for 5 minutes, turning it in the oil. Drain to a plate. Add the chicken thighs to the pan and fry for about 5 minutes until cooked through. Drain to the plate. Cook the squid rings and prawns in the oil, turning the prawns once, until pink. Drain to the plate while cooking the rice.
Add the red pepper, garlic and onion to the pan and fry gently for 5 minutes until softened. Stir in the rice, turning it in the oil for 1 minute. Add the saffron and stock to the pan and bring to the boil. Reduce the heat, cover with a lid or foil and cook gently for about 20 minutes until the rice is cooked through.
Scrub the mussels, scraping off any barnacles and pulling away the beards. Discard any damaged shells or any open ones that don't close when tapped gently with a knife.
Return the chorizo, chicken, squid and prawns to the pan with the peas or beans and mix thoroughly. Scatter the mussels over the top, pushing them down slightly into the rice. Cover and cook for a further 5 minutes or until the mussels have opened. Discard any shells that remain closed. Check the seasoning and serve garnished with lemon or lime wedges.