Boil the potatoes in salted water, rinse in cold water and peel off. Slice. Wash the tomatoes, remove the stalk and dice. Mix the potato slices and tomatoes with the marinade and place in a baking dish. Sprinkle with salt, pepper and basil.
Rub fish fillets with pesto and season with salt and pepper. Place on the vegetables and sprinkle with a little parmesan if you like.