This will help you get started, you would put a method similar to this in your controller and create a view with a password field on it.
public function actionPassword() {
if(isset($_POST['email'])) {
$record=User::model()->find(array(
'select'=>'email',
'condition'=>'email=:email',
'params'=>array(':email'=>$_POST['email']))
);
if($record===null) {
$error = 'Email invalid';
} else {
$newpassword = 'newrandomgeneratedpassword';
$record->password = $this->hash_password_secure($newpassword);
$record->save(); //you might have some issues with the user model when the password is protected for security
//Email new password to user
}
} else {
$this->render('forgetPassword'); //show the view with the password field
}
}