The quintessential ingredients are all here: tomatoes, leftover bread, garlic, and a hint of sherry vinegar.
Make the gazpacho: Cover bread with cold water, and let soak for 15 minutes. Meanwhile, cover garlic with water in a small saucepan, and bring to a boil. Cook for 3 minutes; drain.
Transfer garlic to a blender. Squeeze excess liquid from bread, and transfer bread to blender. Add 2 teaspoons salt, the tomatoes, cucumber, bell pepper, and vinegars. Puree until smooth. With machine running, pour in oil in a slow, steady stream, blending until emulsified. Blend in cold water. Season with salt and pepper. Refrigerate gazpacho until chilled, at least 3 hours (or up to 1 day).
Make the croutons: Heat oil in a medium skillet over medium heat until hot but not smoking. Add bread, and fry, tossing constantly, until pale gold and crisp, 6 to 8 minutes. Using a slotted spoon, transfer bread to a paper-towel-lined plate. Season with salt and pepper.
Divide chilled gazpacho among 6 bowls. Drizzle with oil, and top with croutons just before serving.