Preheat the oven to 425 degrees.
Place the eggplant in a colander and sprinkle salt on it, letting it sit for 5-10 minutes. The excess water inside the eggplant will start to condensate to its surface. Wipe it down with a paper towel.
While the eggplant is sitting, place the spinach, olive oil, and the parmesan cheese into a blender (I like to use my hand held immersion blender) and pulse until it has a pesto consistency.
Place a few discs of eggplant along the bottom of a ceramic baking dish. Spoon some of the spinach pesto on top of each disc.
Next spoon some sauce on top of the pesto on each disc. Repeat until you have 3 layers of eggplant.
Bake, covered, for about 35-40minutes. Then sprinkle the mozzarella on top of the cooked eggplant, cook for 5-10 minutes more until it melts, and serve.