Preheat oven to 375ºF. Line two baking trays with parchment paper. Drizzle with olive oil and spread around with the back of a spoon or offset spatula. Lay eggplant slices in a single layer on the baking trays. Sprinkle with salt. Place trays in oven and bake for about 15 minutes, or until eggplant begins to get soft and lightly browned. Slices should be starting to look translucent when they are done. Remove trays from oven and let cool for a few minutes.

Spread several spoonfuls of tomato sauce on the bottom of a casserole dish: the bigger the casserole, the thinner your lasagna will be. Place eggplant slices, slightly overlapping, over the tomato sauce. Spoon ricotta over the eggplant slices and gently spread it evenly to cover all the slices. Sprinkle shredded mozzarella, then a few spoonfuls of tomato sauce. Begin another layer of eggplant, topped with ricotta, mozzarella, repeat until eggplant is gone. Spoon more tomato sauce on top of last layer of eggplant and sprinkle with remaining mozzarella. Bake for about 20 to 25 minutes, or until the sauce is bubbling around the sides.

Remove casserole dish from oven and let sit for about 10 minutes to set before cutting and serving. Slice into squares and serve while hot. Can be made a day or two in advance, or baked then frozen for up to 3 months.