Wash the fish fillets, pat dry and cut into small pieces. Drizzle with lemon juice, salt and pepper.
Heat the oil in a saucepan and sweat the chopped tomatoes and garlic in it. Simmer for about 10 minutes and season with salt, pepper and sugar. Remove from heat and fold in the basil leaves.
Butter a baking dish and spread half of the tomato sauce in it. Spread the finely chopped redfish and gnocchi on top. Now pour the rest of the tomato sauce over it. Spread the grated parmesan on the casserole. Preheat the oven to 180 degrees and cook for about 30 minutes.