Heat a tablespoon of oil in a saucepan over medium heat. Add the onion, garlic, and celery. Sweat until the onions start to soften. Add the tomatoes. Season with coarse salt. Simmer until the tomatoes start to break down, about 20 minutes.
In the meantime, combine the flour and cheese. Season the mixture with fine salt and black pepper. Dry the fish fillets with absorbent paper. Lightly coat each fillet with the mixture and set aside.
Heat a couple of tablespoons of oil in a frying pan over medium heat. Fry the fillets until golden brown, about 3 or 4 minutes per side. Place the filets on heated serving plates.
Mix the basil into the sauce and spoon the sauce around the fish.