In the bottom of a large bowl, combine the olive oil, lemon juice or vinegar, garlic, mustard, 1/2 teaspoon of salt, and a few grinds of pepper. Add the onion, and corn and toss until coated. Let sit for 10 minutes while you prep everything else.

To the bowl, add the tomatoes, peaches, bread, and half the basil. Toss to combine, adding more olive oil if the bread is too dry, and more lemon, salt, and pepper, to taste. Let the salad sit for about 10 minutes so that the juices can soak into the bread. Give it a toss, then top with the remaining fresh basil and the chickpeas, if using.