To make the marinade. Scatter the fennel seeds in a small frying pan over medium heat and dry-roast until they begin to pop. Transfer to a mortar and pestle and crush roughly. Place the crushed seeds in a small bowl and add the remaining marinade ingredients.
Break the mozzarella roughly with your hands. Smear it with the marinade and set aside for 15-30 minutes to absorb the flavors.
To serve, cut the tomatoes into wedges and plate along with the marinated mozzarella. Drizzle with extra olive oil. Serve along with crusty French bread slices.