use XML::Simple;

# your structure
$FIELDS = {
    'AA' => {
        'Description' => '',
        'Type' => 'Module',
        'File' => 'Sample1.pl',
    },
    'BB' => {
        'Description' => 'Initiator',
        'Type' => 'Methods',
        'File' => 'Sample1.pl',
    },
    'CC' => {
        'Description' => 'Destructor',
        'Type' => 'Methods',
        'File' => 'Sample2.pl',
        'Values' => {
            '1' => 'Ignore',
            '2' => 'Retry',
            '3' => 'Abort',
        }
    }
};

# hash transformation, in-place
my $c;
for my $key (sort keys %$FIELDS) {

    $FIELDS->{$key}->{Label} = $key;
    $FIELDS->{$key}->{No}    = ++$c;

    for my $label (qw(Description Type File)) {
        $FIELDS->{$key}->{$label} = { content => $FIELDS->{$key}->{$label} };
    }

    if (exists $FIELDS->{$key}->{Values}) {

        my $values_hash = $FIELDS->{$key}->{Values};

        $FIELDS->{$key}->{Values} = [
            map {
                { No => $_, content => $values_hash->{$_} }
            } sort keys %$values_hash
        ];
    }
}

# output the XML
print XMLout(
    {
        data => {
            Node => [
                map $FIELDS->{$_}, sort keys %$FIELDS
            ]
        }
    }
);
__END__
<opt>
  <data>
    <Node Label="AA" No="1">
      <Description></Description>
      <File>Sample1.pl</File>
      <Type>Module</Type>
    </Node>
    <Node Label="BB" No="2">
      <Description>Initiator</Description>
      <File>Sample1.pl</File>
      <Type>Methods</Type>
    </Node>
    <Node Label="CC" No="3">
      <Description>Destructor</Description>
      <File>Sample2.pl</File>
      <Type>Methods</Type>
      <Values No="1">Ignore</Values>
      <Values No="2">Retry</Values>
      <Values No="3">Abort</Values>
    </Node>
  </data>
</opt>