This is a question posed to AOPA legal services and their answer in Volume 19, Issue 16 of AOPA ePILOT:

Question 

As a certificated flight instructor, what types of flight training can I give if I do not have a current medical or fly under BasicMed?

Answer

You can give any type of training authorized by your instructor certificate that does not require you to serve as pilot in command or a required crew member. For example, you can give aircraft checkouts, flight reviews if the pilot is still current, and commercial pilot training. You cannot fly with student pilots or give instrument training, complex airplane training for someone seeking an endorsement, or flight reviews if the pilot is not current. You can give sport pilot instruction on the basis of your driver’s license if your FAA medical was not revoked, denied, withheld, or suspended.