Seasoned Skillet: most cast iron skillets require seasoning which means proper oiling of the surface. Rubbing a vegetable oil on the skillet surface is recommended after washing to restore the sheen, secure the non-stick component of the surface and to protect it from moisture. If your skillet is dry, you may need to do this before trying the recipe to avoid excess sticking.
Skillet Size: I'm using a relatively small (9") skillet in these photos - you could use a larger skillet (or two if you have) or work in batches.
Thickness of Eggplant Slices: if you cut the slices thinner than ½" the eggplant will be too soft and start to disintegrate. Better to work with slightly thicker pieces.
Fresh Basil: if you add the basil too soon it will burn (it happened to me a number of times) - you can tuck a few pieces under the cheese if you wish but mostly it works best to top the slices with it once cooked.
The Base: if tomato is not your thing, skip the marinara and consider a pesto base.
The Toppings: the sky is the limit! Switch up the greens (arugula, chard, kale, spinach and the full suite of garden herbs) add sliced veg or pops of fruit if you wish (arugula and cherry is a delicious combo). Try any number of cheese varieties (including vegan) or skip that element all together. Asiago, Parmesan, fontina and provolone would all be classic choices but you could also go with something deeper in the blue cheese family if you wish. We enjoyed a feta/kalamata/spinach variety the other night that was delicious. Peach and creamy ricotta are next. I also experimented with shredded cheese which allowed the marinara to poke through more creating a nice effect.