Combine 2 cups tomato, and 1 cup cucumber, the onion, bread, oil, vinegar, garlic, salt, pepper, and 1/2 cup water in a blender or food processor; cover and blend or process until smooth (blend in batches, if necessary). Transfer to a serving bowl. Stir in remaining tomatoes and cucumber.
Serve immediately or chill up to 2 hours before serving. Garnish with parsley.