Place the lemon juice, olive oil, water, garlic, carrot, pepper and leek in a large frying pan. Season with salt and pepper and bring to the boil. Lower the heat to a simmer and lay the fish fillets close together on top of the vegetables. Cover with a piece of baking parchment, then with a lid or a tray and cook for 6-7 minutes until the fish is cooked - the flesh should be flaking.
Using a fish slice, gently transfer the fish to warmed serving plates. Add the chopped parsley to the cooking liquid then spoon this over the fish and you have your sauce. This is delicious served with some boiled new potatoes and sautéed spinach.