I'm surprised you hadn't discovered Template::Plugin::Dumper yet! For example, in my testing template, I have:

[%  USE Dumper;
  global.foo = global.foo + 1;
  "<pre>"; "global is:\n"; Dumper.dump(global) | html; "</pre>";
  component.foo = component.foo + 1;
  "<pre>"; "component is:\n"; Dumper.dump(component) | html; "</pre>";
  template.foo = template.foo + 1;
  "<pre>"; "template is:\n"; Dumper.dump(template) | html; "</pre>";
%]
[%
  "<pre>";
  USE dumper(indent = 1);
  dumper.dump(uri, env, params, pnotes, cookies) | html
  "</pre>";
%]
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-- Randal L. Schwartz, Perl hacker