Wash the fish, dab dry. Sprinkle with lemon juice and let it steep a little. Peel and finely chop the onion. Clean and wash the fennel and cut it into thin slices. Wash and halve or quarter the tomatoes
Season fish with salt and pepper. Heat the oil in a large pan. Fry the fish in it over medium heat for 5-6 minutes on each side. Remove and keep warm. Fry the onion and fennel in the cooking fat for 10-15 minutes
Wash the rosemary and, except for one thing, pluck. About 5 minutes before the end of the frying time, add the tomatoes to the pan and fry briefly. Add olives, heat up
Season everything with salt and pepper. Place the fish on the vegetables and let it stand for a short time. If necessary, sprinkle with coarse pepper and garnish with the rest of rosemary. Goes well with baguette