Wash and halve the tomatoes and cut out the stalk. Cut the tomatoes into small pieces. Peel and finely chop the onion. Heat 1 tsp. oil in a small pot. Fry the diced onion for about 1 minute.
Douse with white wine. Add the tomatoes. Season sauce with salt, pepper and sugar and simmer covered for 10-15 minutes. Wash the rocket and drain well. Season vinegar with salt, pepper and sugar.
Fold down 1 tablespoon of oil. Wash the fish, dab dry and season with salt, pepper and a little lemon juice. Heat 1 tsp. oil in a coated pan. Carefully fry the fish in it for about 4 minutes, turning it over.
Wash the thyme, shake dry and pluck the leaves. Add the thyme to the fish just before the end of the cooking time. Mix salad and vinaigrette, arrange in a bowl and sprinkle with parmesan.
Arrange the fish on the sauce.