first of all, im not sure what would be the best aproach, but a few come to my mind.
I think the easier would be to load the register form in your admin, remember you can load it from any controller with the service manager, something like
$form = $sm->get('zfcuser_register_form');
and then you can work with it as you would do with any form, sending it to the view, and so.
You would have the full register form, with all the fields you have set as required in your zfcuser.global.php, including the password. I think it is good to set a temp password, and have the user change it later. also you could have its status as unconfirmed until the first password change.
If you dont want an specific field, you can take it out as you would with any form, by means of
$form->remove('element_name');
You would want to check the element names at ZfcUser\Form\Register
Also, remember that if you remove any field, you would have to modify the input filter, otherwise the validation will fail. For this, in your module's bootstrap, you should attach an event listener, something like this:
$em = $e->getApplication ()->getEventManager ();
$em->attach ( 'ZfcUser\Form\RegisterFilter', 'init', function ($e) {
$filter = $e->getTarget ();
//now modify the inputfilter as you need
});
Then, you will have to send the mail to the user. For that i will also use the event manager, at your bootstrap you register a listener for when the user is created, this is by means of
$sm = $e->getApplication ()->getServiceManager ();
$zfcServiceEvents = $sm->get ( 'zfcuser_user_service' )->getEventManager ();
$zfcServiceEvents->attach ( 'register.post', function ($e) {
$form = $e->getParam ( 'form' );
$user = $e->getParam ( 'user' );
//now you have all the info from the form and the already created user, so you can send the mail and whatever you need.
The last step, is to let the user change his password. To do this, i will send him to a module where you show the change password form, that you can retrieve with:
$sm->get('zfcuser_change_password_form');
or directly, sending him to the /user/change-password url that is one of the predefined with zfc-user.
I think this will be the cleanest way.
Another approach
If you dont like it that way, you can use another approach where you create your own form, fill it, save the data to a temp table, send the mail and then...when the user comes to set his password, you build a register form, with the fields pre-filled (and hidden, changing the input type to hidden, or by css) and let him send the form, so while he thinks he is sending just the password, actually he is sending all the registration form, and from here everything is like in normal registration.
For this solution you will also have to use the events, but probably you'd have to take a look at the register event,that is triggered when the form is sent, before the user is saved in the database, so you can modify any data you could need.
$zfcServiceEvents->attach ( 'register', function ($e) {
$form = $e->getParam ( 'form' );
And also you should take a look to the already mentioned init event, where you can retrieve the form before you show it to the user, and prefill any data from the temp table.
$events->attach ( 'ZfcUser\Form\Register', 'init', function ($e) {
$form = $e->getTarget ();
//now you set form element values from the temp table
Probably this is so confusing, but i hope you at least get a clue of where start from!