Preheat the oven to 300 degrees F. Spread the bread out on a rimmed baking sheet and toast until golden brown, about 10 minutes. Let cool.
Put the vinegar, 1/4 teaspoon salt, the tomatoes and their juices and the garlic in a large bowl and toss together. Set aside.
Heat the oil in a large skillet over high heat. Add the corn and spread in a single layer. Cook until blackened in spots, about 3 minutes. Add the chiles and onions and cook, stirring occasionally, until lightly browned and crisp-tender, about 2 minutes. Transfer the mixture to the bowl with the tomatoes.
Add the bread to the bowl and gently stir together; season with salt. Stir in the cilantro and serve.