External Apple Drive

If this is an SSD drive, your files are gone.

If it is a mechanical drive, only the first 1,000 blocks (which includes the directory area) can be erased in the minute or so a typical Erase takes. To completely erase the drive takes all afternoon.

So your files (but NOT their names) are likely still on the drive. If this was a boot drive, it also contains over 350,000 files (not an exaggeration) that are the components of MacOS. Finding what you want, if not already damaged or re-used, will be difficult. Do not write anything to the drive, or store any files on it, or the parts of your files still present may be overwritten.

One commonly recommended tool for doing this is Data Rescue from Prosoft. It can make forays onto an erased or unmountable drive to look for parts of lost files. But it will NOT restore them to the same drive -- you must have a different drive on which to restore any files or fragments it finds. And the names are lost when the directory is erased..

What exactly do you mean by "Apple external drive"? There are no external drives made by Apple; however, there a lots of them made by other mfr's.

And, if the drive was erased and reformatted, chances are very slim to recover anything. You can try a file recovery service or software, but there is no guarantee and the service is not cheap.

What's the make and model? Although it really is not that important: if it's been erased and reformatted, nothing on it may be recoverable.