Slice eggplants into 1/2-inch rounds. Sprinkle with kosher salt and let sweat for 30 minutes, then pat dry with paper towels.
Preheat oven to 400°F (200°C). Line two large baking sheets with parchment paper and lightly coat with cooking spray.
Set up a breading station with three shallow bowls: one with all-purpose flour, one with whisked eggs and milk, and one with panko breadcrumbs, Italian seasoning, and garlic powder.
Coat each eggplant slice in the flour, dip into the egg mixture, and firmly press into the seasoned panko breadcrumbs.
Arrange the breaded slices on the prepared baking sheets in a single layer. Bake for 20 minutes, flipping halfway through, until golden brown and crispy.
Spread 1/2 cup of marinara sauce evenly over the bottom of a 9x13-inch baking dish. Place half of the roasted eggplant slices in an even layer.
Top with 1 1/4 cups of marinara sauce, 1 cup of shredded mozzarella cheese, and 1/2 cup of grated Parmesan cheese. Repeat the layers with the remaining eggplant, 1 1/4 cups of sauce, and remaining cheeses.
Bake the assembled casserole for 20 to 25 minutes until the cheese is melted and bubbling. Garnish with fresh basil leaves before serving.