1.Score the skin of the fish three times at the thickest part. Heat half the oil in a large frying pan; cook fish until browned on both sides and just cooked through. Transfer fish to a plate; cover to keep warm.
2.Meanwhile, remove rind from lemon using a zester. Squeeze juice from lemon (you will need about 2 tablespoons). Combine rind, raisins, juice, nuts, parsley and remaining oil in a small bowl; season to taste with salt and freshly ground black pepper.
3.Divide spinach among serving plates, top with fish and lemon raisin salad. Drizzle with any remaining dressing.