As per the comments, getting the cargo to spawn and register might be a problem for some. Not sure if it's bad luck or glitchy. It's also possible it will only spawn once per playthrough, meaning a second playthrough is required if you miss it. This solution is just my own experiences.
It seems like this is a specific, random event that you'll come across as you transition through sectors on missions. I'll add as much information as I can just in case it helps.
I was a few missions into Phase 2, on the mission "Investigate Oumuamua". It was in the first sector after jumping from Athena, Hestia Spiral Arm Accretion. There were no enemies. An optional objective appeared to "Retrieve Item".
A message appeared from the Wing Commander at the top of the screen:"There's a dropped cargo pod of essential resources in your current sector. If you can get them back to base, it would mean a few extra credits!"
I don't recall seeing this message any other time, so if you see this, drop everything and grab that cargo! (Edit - per the comments, it appears this is not the specific
The achievement won't unlock until the mission completion screens back at Athena Base.
There are several random retrieval missions that don't trigger this achievement. Just keep going for the purple optional objectives when you see them and hopefully you'll eventually find the right cargo.
You can attempt to farm these missions, as suggested by Redders 420
who commented:One thing I did figure out is if you come through the warp portal and don't get a recovery side mission, immediately turn around and warp back into the area you just came from and then warp back in again. The side missions seem to be random so I just kept entering the area until I got the correct mission and recovery item.
They all look similar but this is the cargo in question that unlocked it for me (orange item in bay on bottom-left of the ship):