I grew up with this! My dad (independently) invented this. The eggplant slices serve as the pizza "dough". Sometimes we peeled the eggplant, and sometimes we didn't. We did usually add chopped mushrooms to the mix, and sometimes just a little spicy pepper flakes or Tabasco. Before cooking the eggplant we usually squeezed lemon juice over the eggplant to minimize darkening.
I was about to post our recipe for this, but I see you got here first. It's great! And it is indeed flexible.