For the best flavor, use high-quality, extra-virgin olive oil and fresh mozzarella. If you don't have a broiler, you can toast the baguette slices in a toaster oven or on a grill pan. The tomato mixture can be prepared ahead of time and stored in the refrigerator for up to 4 hours. Allow it to come to room temperature before serving. A drizzle of balsamic glaze can add a touch of sweetness and visual appeal.