By default, Dancer uses a simple templating system that has syntax that is very similar to Template::Toolkit. However, you can only pass scalars and you don't have other control stuff (like if statements, loops, etc.). If you try to pass an array or hash to the template with the default templating system choice, the variable in the template will only have the array reference or hash reference.
In order to use Template::Toolkit, you need to have template: template_toolkit in your config.yml file or set template => 'template_toolkit'; in your code itself. Look at the Dancer::Config, Dancer::Template and Dancer::Template::Simple documentation for more details.