gistfile1.php

<?php

  class Foo
  {
      protected $labelCallable;
      
      public function setLabelCallable($labelCallable)
      {
          $this->labelCallable = $labelCallable;
      }
      
      ...
      
      public function doSomething()
      {
          // find your object...
          $object = ...;
          
          if (is_callable($this->labelCallable)) {
              $label = $this->labelCallable($object);
          }
      }
  }
  
  
  // So in your form you can do something like this :
  
  $this->add(array(
    'name'       => 'someName',
    'type'       => 'MyNamespace\Form\Element\EntitySelect',
    'attributes' => array(
        'required' => true
    ),
    'options'    => array(
        'label'          => 'Select element Label',
        'empty_option'   => '--- Choose Entity ---',
        'object_manager' => $this->getEntityManager(),
        'target_class'   => 'MyNamespace\Entity\TargetEntity',
        'label_callable' => function($object) {
            return $object->propertyOne + ' - ' + $objectPropertyTwo;
        }
    )
));