With a pestle and mortar, grind the walnuts until fine. Pop the chillies into a blender with 100ml of water and blitz to a purée. In a large pan of salted water, boil the potatoes for about 15 minutes until cooked through. Dry in a colander for a few minutes, then return to the pan, dress with olive oil and season.
Put a glug of olive oil in a small frying pan over a medium heat. Fry the olives and mint until lightly crispy. Add to the potatoes.
Place the chicken between 2 sheets of greaseproof paper and bash with a rolling pin or a heavy pan until flattened and an even thickness. Season well, drizzle with olive oil and place in the fridge until needed.
In a non-stick pan over a low heat, gently fry the onion and garlic in a good glug of oil for 20 minutes, or until soft and sticky. Stir in the blitzed chilli and cook for a few more minutes before adding the breadcrumbs. Stir in the milk and cook for about 4 minutes, until the sauce thickens, adding a splash of water, if needed. Stir in the ground walnuts and Parmesan, simmer for a further 7 minutes, then season and keep warm while you cook the chicken.
Heat a griddle pan until screaming hot and add the chicken, skin-side down. Cook for around 4 minutes until the skin is lovely and golden, then turn and cook on the other side for 3–4 minutes until cooked through.
Serve the chicken on the sauce with the potato salad on the side. Add a squeeze of lemon and some extra sliced chilli, if you like.