Place the bread slices in a bowl, add water to cover and let stand until soft, 3-5 minutes. Remove the bread and squeeze it dry with your hands.
In a blender or a food processor fitted with the metal blade, combine the soaked bread, onion, garlic, cucumber, most of the tomatoes and 1 of the bell peppers. Process until smooth or chunky, as you like. Pour into a bowl.
Finely chop the remaining tomatoes and the bell pepper and stir them into the bowl. Then stir in the olive oil and vinegar and season to taste with salt and pepper. If the soup is too thick, add a little ice water or a mixture of ice water and tomato juice. Cover and refrigerate until well chilled, or for up to 3 days.
FOR CROUTONS: Cut the bread slices into 1/2-inch (12-mm) cubes. In a large sauté pan over medium-high heat, warm the olive oil. Add the garlic and sauté, stirring, for 1 minute. Add the bread cubes and sauté until golden brown on all sides, 4-5 minutes. Using a slotted spoon, transfer the croutons to paper towels to drain.
Ladle the soup into chilled bowls, top with the croutons and serve.
Recipe reprinted by permission of Weldon Owen. All rights reserved.