box_list => [
    {
        box_name => 'irgendein name',
        box_links => [
            { link => 'linktext1' },
            { link => 'linktext2' },
        ]
    }
]

my $stmt_box_name = 'SELECT box_name FROM navibox';
my $stmt_links = 'SELECT id,link_titel,link,categorie,box_name,option,content FROM navigation WHERE box_name=?';

my $sth_box_name = $dbh->prepare( $stmt_box_name ) or die $dbh->errstr;
my $sth_links    = $dbh->prepare( $stmt_links ) or die $dbh->errstr;

$sth_box_name->execute or die $dbh->errstr;

my @boxes;

while( my ($box_name) = $sth_box_name->fetchrow_array ) {
    $sth_links->execute( $box_name );

    my @links;
    while( my $hashref = $sth_links->fetchrow_hashref ) {
        push @links, { link => $hashref->{link} };
    }

    push @boxes, { box_name => $box_name, box_links => \@links };
}

$template->param( box_list => \@boxes );