FWIW, the Template option in the constructor should be a sref; TmplOptions and TmplParams should both be a href. Here's what I played with. Don't forget your template:-).

#!/usr/bin/perl

BEGIN { $MIME::Lite::VANILLA = 1; }

use strict;
use warnings;
use MIME::Lite::TT;
use Data::Dumper::Concise;

my $template = <<TEMPLATE;

This is a template.
my name is [% me %].

TEMPLATE

my %params  = (name => 'me');
my %options = (EVAL_PERL => 1);

send_email();

sub send_email {
    my $msg = MIME::Lite::TT->new(
        From        => 'me@xyzzy.com',
        To          => 'me@xyzzy.com',
        Subject     => 'test message',
        Type        => 'multipart/mixed',
        Template    => \$template,
        TmplOptions => \%options,
        TmplParams  => \%params,
    );
    $msg->attach(
        Type        => 'AUTO',
        Path        => '/tmp/test.pl',
        Readnow     => 1,
        Filename    => 'test.pl',
    );
    $msg->stringify;
    $msg->print(\*STDOUT);
}
exit;

__END__
[download]

And a very simple test.pl to put in /tmp

#!/usr/bin/perl
# test.pl
use strict;
use warnings;

print "This is a test. Please standby for instructions\n";
[download]