After I wrote the post I've just found a solution, here is my code:
This the renderForm inside my controller:
public function renderForm() {
$fields_list = array(
'id_test' => array(
'title' => $this->l('Col1'),
'width' => 25
),
'field1' => array(
'title' => $this->l('Col2'),
'width' => 25
),
'field2' => array(
'title' => $this->l('Col3'),
'width' => 25
),
);
$helper = new HelperList();
$helper->shopLinkType = '';
$helper->simple_header = true;
$helper->identifier = 'id_test';
$helper->show_toolbar = true;
$helper->title = 'Boomprice Used';
$helper->table = 'boomprice_used_cod';
$database_data='';
$sql = 'SELECT * FROM '._DB_PREFIX_.'table_name';
$results = Db::getInstance()->ExecuteS($sql);
if (empty($results)) {
$database_data= 'Nothing';
} else {
$database_data = $results;
}
return $helper->generateList($database_data, $fields_list);
}
I hope this code will help someone.