Preheat oven to 400.
Line baking sheet with paper towels + arrange eggplant in 1 layer. Sprinkle w/ kosher salt + let sit 30 mins to draw out bitterness (optional but recommended).
Blot dry. Remove eggplant + line baking sheets w/ parchment paper.
Brush both sides of eggplant w/ about ¼ c olive oil + arrange in 1 layer.
Bake 20–25 mins, flipping halfway, until golden + tender.
Lower oven to 350.
In a bowl, toss breadcrumbs w/ ¼ c olive oil. Add pinch of salt if needed + optional parmesan.
Spread thin layer of tomato sauce in a 13x9 baking dish.
Layer cooked eggplant over sauce.
Spread more sauce over top.
Repeat with another layer of eggplant + sauce.
Top w/ mozzarella, then breadcrumb mixture.
Bake 15 mins until warmed through + cheese is melted.
Broil for a few seconds if needed to brown the top.
