Preheat the oven to 170C/325F (fan).
Mix together the salt, garlic salt, black pepper, white pepper, and paprika. Rub onto the skin of the chicken thighs.
Heat the oil in a large, wide cast iron pan (or a heavy-based, ovenproof large frying pan) over a medium-high heat.
Place the chicken thighs in the pan, skin-side down. Cook for 4-5 minutes until the skin is golden brown. Turn oven and cook for another couple of minutes.
Remove the chicken from the pan and place on a plate.
Add in the chopped onion, celery, and red pepper. Cook for 3-4 minutes, until the vegetables start to soften.
Add in the chorizo and cook for a further two minutes.
Add in the oregano, garlic, and tomato puree. Stir, then add in the rice. Stir again to coat the rice in the oil.
Pour in the wine and stock, give everything a stir, then place the chicken, skin-side-up in the rice.
Arrange the chopped tomatoes around the chicken and the lemon slices on and around the chicken.
Place a lid on the pan (or cover tightly in foil) and place in the oven for 35-40 minutes, checking on the rice a couple of times in the last 10 minutes, until the rice is tender.
Take out of the oven and sprinkle with parsley before serving.