1 (14.5-ounce) can diced tomatoes with their juice
2 zucchini, cut into 1-inch rounds
2 summer squash, cut into 1-inch rounds
2 tomatoes, cut into wedges
1 large Japanese eggplant, cut into 1-inch rounds
1 red onion, peeled and cut into 1-inch wedges
1 potato, peeled and cut into 1-inch cubes
3 garlic cloves, minced
1/4 cup extra-virgin olive oil
1 1/2 teaspoons salt
1 teaspoon freshly ground black pepper
1 teaspoon dried oregano
4 to 6 slices toasted sourdough bread, optional for main dish