Put all four of the fish into a large Ziploc bag (or four individual bags) and stuff the fish with spring onions, drizzle over the lemon juice, rub in the garlic, thyme and lemon zest with a little black pepper.
Remove all air and pop in the fridge to marinate overnight,alternatively stuff the fish with spring onions, put the fish in a shallow bowl, drizzle over some lemon juice and rub in the garlic, the thyme, lemon zest and some salt and pepper, cover loosely with cling wrap and allow to marinate in the fridge overnight.
Remove from the fridge, coat the fish with flour, shaking off the excess and fry on both sides until golden brown.
Remove from the pan with a slotted spoon and allow to drain on absorbent paper.
Heat the peanut oil and butter in pan, fry the onions until they are translucent and soft, stir in the tomatoes and cook briskly for a couple of minutes before adding the turmeric, the white wine, the chilli, the fish stock and the sugar – stir well and bring to the boil.
Simmer gently and cook, covered for around 10 minutes before adding the fish and cooking until the fish is done – this normally takes about 15 minutes but you’ll have to check yourself here.
Add the mango, stirring it in and allow it to warm right through, check and correct the seasoning.
Place the fish on a serving platter, pour over the sauce and garnish with the chopped parsley to serve immediately.