Preheat the oven to 400 degrees F. Sprinkle the eggplant slices with salt and let them sit for 15 minutes to release moisture. Pat the slices dry with a paper towel.
Brush both sides of the eggplant slices with olive oil and arrange them in a single layer on a baking sheet. Bake for 20 minutes, flipping halfway, until they start to soften and turn light golden.
Spread 1/2 cup marinara sauce in the bottom of a 9x9 inch baking dish. Add a layer of eggplant slices, then sprinkle with some mozzarella, Parmesan, and a pinch of oregano. Repeat the layers until all ingredients are used, ending with sauce and cheese on top.
Mix the breadcrumbs with the remaining olive oil and sprinkle evenly over the final cheese layer. Bake uncovered for 25 minutes until the top is browned and the sauce bubbles at the edges.
Remove from the oven and let the casserole rest for 5 minutes. Scatter fresh basil leaves over the top before serving.