With how potent fentanyl is, it would make sense if avocados are being hollowed out (where the pit is), and having compressed fentanyl placed there. On a scanner, it would look like a normal avocado. This would also explain both why the [media] is so focused on avocados coming in from Mexico, as well as the listeria like symptoms from "contaminated" avocados.
The symptoms of listeria and fentanyl exposure are nearly identical and I posted about it a while back.