my $res = $self->{_DB}->execute(
              sql => 'SELECT * FROM customers WHERE email = ?',
              method => 'fetchrow_hashref',
              data => [$form_data->{email}]);

# OR something like this if you know it will return more results

my $STH = $self->{_DB}->execute(
              sql => 'SELECT * FROM customers WHERE email = ?',
              data => [$form_data->{email}]);

while($row = $STH->fetchrow_hashref()){
    # ....
}