The idea with all of this, is when this cgi is executed, every processed url appears in a new tab

Sending multiple HTML documents to the browser will not achieve this...

I think I would approach this by adding all the URLs into an array and passing a reference to the array into Template to process a single template file. In the template file, have a some Javascript and a FOREACH loop that adds the Javascript calls to window.open for each URL.

Rather than processing the template file multiple times within Perl, assemble the data in Perl and pass that once to the template file and let that do the iterations.