Heat a dry (seasoned) cast iron pan on medium and add eggplant rounds.  As they cook the eggplants shrink a bit so I continue adding more rounds or halved rounds to speed cooking time.

As they begin to brown I turn the rounds with a narrow spatula.

When the eggplant rounds have been toasted and cooked down to about 1/4 inch, I dab a very small amount of olive oil on each side and toast a
minute more on each side.  The olive oil creates a beautiful sheen and adds flavor but it also makes the salt or seasonings you may choose to add stay on the eggplant. I like using a long-handled silicone brush.