To achieve this, add the following to your controller:
sub auto : Private {
my ($self, $c) = @_;
$c->stash(template => 'my_default_template.tt') if ($c->controller eq $self);
}
Change my_default_template.tt to whatever and you're done. Also note that once you have set this up, you can still set the template in actions as usual using:
$c->stash->{template} = 'hello.tt';
