Wash and dry tomatoes. Working with 1 tomato at a time, thickly slice tomato. Season each slice with salt and freshly ground black pepper, then place slices back on top of each other to reform each tomato as a whole.
For the dressing, whisk oil, vinegar, sugar and salt and pepper together until well combined. Stir in the olives and pine nuts.
Scatter the basil over 4 serving plates. Tear mozzarella in half and arrange on serving plates with tomatoes. Spoon over the dressing and serve with crostini.