<?php

$myArr = [0 => 0, 1 => 0, 2 => 0, 3 => 1, 4 => 1, 5 => 0, 6 => 0];

$counter = 0;
$in_group = false;
$arrayGroups = [];
foreach ($myArr as $val) {
    if ($val == 0) {
        if ($in_group) {
            $arrayGroups[$counter]++;
        } else {
            $in_group = true;
            $counter++;
            $arrayGroups[$counter] = 1;
        }
    } else {
        $in_group = false;
    }
}

print_r($arrayGroups);