Heat the oven to 350°F. Cut the bread crosswise into slices about 1 inch thick. Put them on a baking sheet and toast in the oven, turning once or twice, until they are crisp and golden, about 15 minutes. Let cool and store if you like, tightly covered, for up to 2 days.
While the bread is toasting, core and roughly chop the tomatoes and put them and their juices in a large bowl. Add the mozzarella, oil, and vinegar; sprinkle with salt and lots of pepper and toss several times to combine well.
Fill a medium bowl with water, add the toasted bread, and soak until the pieces start to absorb some water to soften, 2 to 3 minutes. Gently squeeze the water out of the croutons and crumble them into the salad.
Toss well to combine the ingredients and let the salad sit for 15 to 20 minutes. Toss with the basil, taste and adjust the seasoning, and serve.