Whisk the buttermilk and salt in a bowl until combined. Add the chicken pieces and mix until coated in the buttermilk. Cover and chill in the fridge for at least 4 hours, and preferably overnight.
When the chicken has soaked in the buttermilk, remove the bowl from the fridge to allow it to return to room temperature before cooking. Preheat the oven to 200C/180C Fan/Gas 6.
Mix the flour, lemon zest and all of the spices in a bowl until well combined.
Lift the chicken pieces out of the buttermilk, scraping off as much of the mixture as you can, then roll them in the spiced flour until completely coated.
Heat the oil in a large, heavy-based, ovenproof frying pan to a depth of 1cm/½in, until a breadcrumb sizzles and turns golden-brown when dropped into it. (Caution: Hot oil can be dangerous. Do not leave unattended.)
Add the chicken pieces to the hot oil, in batches, placing them skin-side down. Fry for 2-3 minutes on each side, or until golden-brown all over.
Transfer the pan to the oven and continue to cook for 12-15 minutes, or until the chicken is cooked through and the skin is crisp. (The chicken is cooked through if the juices run clear when the chicken is pierced in the thickest part with a skewer.) Remove from the pan using tongs and set aside to drain on kitchen paper. Keep warm.
Cook the remaining batch of chicken pieces in the same way.
Meanwhile, for the salsa, heat the sugar in a heavy-based frying pan over a high heat, without stirring, until it melts to form a golden-brown caramel. Swirl the pan occasionally to stop the caramel from catching on the bottom of the pan.
Add the chopped tomatoes to the pan, stir to coat them in the caramel, and cook for 1-2 minutes, or until just softened.
Add the chillies, sweetcorn, red wine vinegar and lime juice and continue to cook for 6-8 minutes, or until the tomato has completely broken down. Stir in the parsley, then season, to taste, with salt and freshly ground black pepper.
To serve, pile the chicken pieces onto a serving platter. Serve the salsa in a bowl alongside.