get '/bar' => sub {
  my $self = shift;
  if( $cond ) {
    $self->stash( one => 23 );
  }
  else {
    $self->stash( two => 42 );
  }
  $self->render('baz');
}

app_start;
__DATA__
@@ baz.html.ep
<%= $one %> or <%= $two %>.