Prepare the eggplant by trimming the tops and bottoms and slicing them lengthwise into 1/4 inch thick pieces.

Arrange the eggplant slices on a rimmed baking sheet, spray with nonstick cooking spray, and season with salt and pepper on both sides.

Preheat the grill to medium-high heat and lightly oil the grates.

Place the seasoned eggplant on the grill in an even layer and cook, flipping occasionally, until softened with nice grill marks, about 10 minutes.

Remove the grilled eggplant from the grill and transfer back to the rimmed baking sheet.

Set the grill for indirect cooking, heating it to a temperature between 425°F to 450°F.

In a medium bowl, combine ricotta, egg, and grated Parmesan cheese thoroughly.

In a 10-inch cast iron skillet, spread a heaping 1/2 cup of marinara sauce on the bottom. Layer the grilled eggplant over the sauce with 5-6 slices.

Top with a third of the basil, mozzarella, and ricotta mixture. Repeat the layers twice more, starting with the sauce and ending with the cheese, ensuring even distribution.

Cover the last layer completely with the remaining marinara sauce.

Tightly cover the skillet with foil and transfer it to the grill's indirect side, closing the lid.

Grill for 40 minutes, then remove the foil and close the lid, cooking for an additional 10 minutes until the sauce has tightened.

Let sit for 10 minutes, then top with remaining basil before cutting into wedges.