To make the sauce, in a sauté pan, heat 2 tablespoons of the extra virgin olive oil over medium heat. Add the onion and cook, stirring occasionally, until softened and translucent, about 8 minutes.
Add the paprika, garlic, finely chopped pistachio nuts, butter and cook, stirring often, for 3 minutes. Add the tomatoes, lemon zest and wine and bring to a slow boil, stirring occasionally, until thickened, 10-15 minutes. Season generously with salt and pepper.
Keep warm over low heat.
Meanwhile in a large frying pan, heat the remaining 2 tablespoons of extra virgin olive oil over medium heat. Season the fish with salt and pepper, add to the pan, and cook, turning once, until browned on both sides, about 3 minutes on each side.
Pour the sauce over the fish, and simmer until the fish is opaque throughout, about 5 minutes longer. Transfer to a serving dish or individual dishes, and garnish with chopped parsley and lemon slices. Serve at once.
