As the article said, zeroing the drive isn't sufficient, so if you're looking for a secure erase, you'll need to do something else as described in the article, or this is my preferred method:
-turn on FileVault, set a password (do not store the encryption key with Apple), allow encryption to complete (this will take a number of hours).
-boot to recovery mode (hold down command and r keys while starting up) and open Disk Utility, select your drive on the left, choose erase/reformat (this will erase the FileVault encryption key which makes the data inaccessible).
-quit Disk Utility and follow the prompts to install an OS.
-turn on FileVault, set a password (again, do not store the encryption key with Apple), and allow encryption to complete.
Now your data has been encrypted and then erased, then the drive has been encrypted again, which ensures that no one can recover the original key, thereby making your “old” data as secure as FileVault is, which to my knowledge, has not been cracked.
If you want to go over the top with security, then combine the method I described with babowa’s method (I’ve made some changes to it): erase the SSD, install an OS, fill up the SSD with any larger, non-personal media files until it is about full. Then erase it and install an OS. Fill it again with different, larger size media files (or any file that is larger so the process is faster) and erase it and install an OS again. Do that a third time and your original files should be pretty much unrecoverable.
