Using helper function to execute FetchXML request is great.
The code below is retrieved from this blog, and all I had to do is to add extra logic when parsing the XML result because I want to grab the attributes from the related entity as well.
To use it you just need to do it like this (synchronous)
If it's asynchronous the last bit will be:
The parsed result object can be queried like this:
Hope this helps,