If the monkfish is not filleted, carefully peel it from the middle bone. Cut into medallions and arrange in a baking dish.
Season the monkfish with salt and lemon juice. Drizzle with 3 tablespoons of olive oil and sprinkle with rosemary sprigs and finely chopped parsley.
Peel the tomatoes, remove the juice and seeds, then cut the flesh into small pieces. Arrange the tomato pieces around and on top of the monkfish.
Halve the olives and scatter them over the dish along with the capers and their liquid. Drizzle with the remaining 2 tablespoons of olive oil and remaining lemon juice.
Preheat the oven to 200 °C (400 °F) with top and bottom heat, no convection. Bake the monkfish for 25 minutes until the fish is cooked through.
Drizzle the monkfish with the cooking liquid that has formed in the dish and let rest for 5 minutes in the switched-off oven.
Serve hot, spooning the cooking liquid over each portion.