Preheat the oven to 220°C, fan 200°C, gas 7.
Tip the potatoes on to a baking tray and gently crush. Sprinkle with 1 tablespoon oil, half a teaspoon of caster sugar and a small pinch of salt. Roast for 30 minutes.
Meanwhile, fry the onion in 1 tablespoon of olive oil with the mixed herbs and garlic, until softened. Add the wine and cook until most of it has been absorbed. Add the tomatoes and simmer for 5 minutes. Tip into a food processor, add the roasted peppers and blitz until smooth. Return to the pan and add the lemon juice, remaining sugar and capers. Warm through.
Season the cod and fry in 1 tablespoon of oil for 4 minutes on each side until cooked through. Serve with the crushed potatoes and sauce, garnished with the basil.