I've used a stack to keep track of opening/closing li tags. 
#!/usr/bin/perl

use strict;
use warnings;
use HTML::TokeParser::Simple;

my $html = do{local $/; <DATA>};

my $p = HTML::TokeParser::Simple->new(\$html)
 or die "can't parse string: $!\n";

while (my $t = $p->get_token){
  last if $t->is_end_tag('span');
}

my ($match, @li_stack);

while (my $t = $p->get_token){
  if ($t->is_start_tag('li')){
    push @li_stack, 'li';
  }
  if ($t->is_end_tag('li')){
    if (@li_stack){
      pop @li_stack;
    }
    else{
      last;
    }
  }
  $match .= $t->as_is;
}

print "$match\n";

__DATA__
<li><span class="title">Title</span><ul><li>one</li><li>two</li></ul> 
+MATCH HERE </li>

[download]
output: 
<ul><li>one</li><li>two</li> MATCH HERE

[download]
update:
Added output.

uptdate 2
see ikegami's reply below.

In reply to Re^3: simple regex help by wfsp
in thread simple regex help by nmerriweather

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.