Preheat oven to 380 degrees.
Slice eggplant vertically in to ¼ in. slices and salt each side generously. Allow eggplant slices to sit for 20 mins. to get rid of excess water in the eggplant.
In the meantime, sauté mushrooms in olive oil and sea salt until softened. Once done, set aside. Prep baking pan (with sides, mine is 8x8) with parchment paper and then coat bottom of pan with marinara sauce until covered.
After 20 mins., pat eggplant dry lightly on both sides and begin layering. Lay eggplant slices, top with sautéed mushroom, basil, and spoon another layer of marinara on top, covering eggplant, mushroom, and basil completely. Start your second layer, ensuring it is lying directly on top of the first. Add mushrooms, basil, marinara, and repeat until finished. Smother layers with marinara sauce and place in oven for about 1 hour (or 1 hour and 15 mins. depending on strength of oven).
Once eggplant is completely fork tender and caramelized, take out of oven and allow to cool.