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 and the vegetables to warmed serving plates.
Spoon the cooking liquid over the fish.
Garnish with some chopped parsley. This is delicious served with some boiled new potatoes and sautéed spinach.