Pass array as query string
If you want to pass that data structure using PHP's URI format (which is what your attempt looks like), it would look something like:
data[0]=something&data[1]=another_thing&data[2]=4&data[3][iam]=anobjectYou are probably better off just passing the JSON itself though. Take the JavaScript object and run it through JSON.stringify() and encodeURIComponent() to get:
data=something%2Canother_thing%2C4%2C%5Bobject%20Object%5DThen you would use querystring.parse(), extract the data parameter from it, then run JSON.parse() on that value.