Preheat oven to 200°C (390°F). To make the Campari dressing, place the Campari, lemon juice and sugar in a bowl and stir until the sugar is dissolved. Add the oil and stir until just combined. Set aside.
Place the fennel, witlof, mint and chervil in a bowl and toss to combine. Set aside.
Place the salt, pepper and sesame seeds in a bowl and stir to combine. Brush the skin side of the fish with oil and press into the sesame mixture. Place the fish, skin-side down, on a lightly greased baking tray. Bake for 10–12 minutes or until cooked through and the skin is crispy. Arrange on plates with the fennel and witlof and drizzle over the Campari dressing to serve. Serves 8.