Heat a splash of the olive oil in a 34 to 36cm paella pan or large shallow casserole dish over a medium to high heat. Season the chicken, add to the pan and brown all over (this will take 15 to 20 minutes)
Once well browned, transfer the chicken to a plate and set aside. Add the remaining olive oil to the pan, turn down the heat to low medium, then fry the onion and beans with a pinch of salt for 8 minutes until softened.
Stir in the toasted saffron and both types of pimentón and cook for a minute until fragrant, then stir in the tomatoes and garlic. Pour in the chicken stock. Bring to the boil, then sprinkle over the rice in an even layer, using a wooden spoon to stir it into the liquid. Stir only once – you’re aiming to create a crust (see Notes) on the bottom of the pan. Poke the chicken pieces into the rice with the herbs, bring back up to a fast simmer, then bubble over a medium heat, uncovered, for 10 minutes.
Turn down the heat to low, simmer for another 5 minutes, then add the prawns in the spaces between the chicken pieces and cover the pan with a double layer of foil, tucking in the edges to seal the steam inside. Cook for a further 5 minutes, then take the pan off the heat and set aside, still covered, for 5 minutes to let the rice steam.
Sprinkle over the chopped parsley, then serve the paella with lemon wedges for squeezing, some crusty bread and a nice glass...or 2...of Spanish red wine!!