Preheat oven to 400 degrees. Spray a casserole dish or 9x13 inch pan with nonstick spray, set aside.
Start by removing the stems and heel of the eggplant, then slice the eggplant into ¼-½ inch slices lengthwise from root to tip (you should get about 16 slices total). Sprinkle kosher salt on both sides of the eggplant slices and let them sit on a wire rack for 20 minutes (this will help draw out the moisture). Either wipe off the salt from the eggplant using a paper towel or rinse it off and pat dry.
Place the eggplant on a lightly greased baking sheet and bake in preheated oven for about 20 minutes to soften the eggplant; set aside to cool slightly.
Meanwhile, make the filling. In a large bowl, stir together the ricotta, egg, Parmesan cheese, and Italian seasoning.
Spread ½ cup of marinara sauce on the bottom of the prepared pan. Cover with a layer of the roasted eggplant (half the eggplant), then top with half of the ricotta mixture, half of the shredded mozzarella, and spread on ½ cup of marinara sauce. Repeat the layers, ending with the mozzarella on top.
Bake for 30-35 minutes, or until the cheese on top is browned and bubbling. Let stand for 10 minutes, then top with fresh basil (optional), slice and serve!
