1. For the tomato jam, combine the tomatoes, sugar, anise and a pinch of salt in a medium saucepan and bring to a boil over medium-high heat. Reduce the heat and simmer, stirring and scraping the bottom occasionally, until the mixture reaches a jam-like consistency, about 40 minutes. Cool to room temperature, about 10 minutes.
2. For the salad, in a large bowl, stir together 1/4 cup of the tomato jam, the balsamic, 2 tablespoons olive oil and 2 tablespoons fennel fronds. Add the sliced fennel and watercress, toss together with the dressing and season with salt. Transfer the salad to a platter and scatter with the mozzarella.
3. Preheat a grill or grill pan to medium-high. Lightly brush the baguette slices with the remaining 1 tablespoon oil and grill until lightly toasted, about 1 minute per side. Transfer to a plate. Spread the toasts with the remaining tomato jam and sprinkle with the remaining 1 tablespoon fennel fronds.