Rinse the fish fillets, pat dry, sprinkle with lemon and pepper seasoning on both sides and drizzle with lemon juice. Set aside for at least 1 hour.
Preheat the oven to 190 C / Gas 5.
In a large saucepan, combine the carrots, onion, leek, parsley root and celeriac, pour in few tablespoons water, cover and simmer for 10 minutes. Add the tomatoes and simmer, uncovered, until the sauce thickens. Stir in garlic and basil. Add chopped parsley and season with salt and pepper to taste.
Arrange a layer of 1/2 vegetables on the bottom of baking dish, place fish fillets on top and cover with remaining vegetables. Sprinkle with grated cheese if desired.
Bake for 35 minutes. If you top the dish with cheese, bake it covered then uncover for the last 10 minutes.