In that case I'm not sure. The following works for me:

#!/usr/bin/perl

use feature qw(say);
use Data::Dumper;

$cliParms = {
  'tcl_defs' => {
    my_var1 => 'a',
    my_var2 => 'b'
  }
};

my %my_tcldefs = %{$cliParms->{'tcl_defs'}};

say Dumper(\%my_tcldefs);
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Could you post the code that's currently failing for you?

P.S. I'm not Dave (davido).