Preheat the oven to 375F. Slice the eggplant into 1/2" slices lengthwise. Place the slices on a large baking sheet and generously season both sides with salt. Let them sit for 20 minutes (the bitter juices will release for better taste and a less watery lasagna).
Meanwhile, start prepping the other ingredients. Add the beef to a skillet over medium-high heat and cook until browned (about 8 minutes). Stir in the marinara sauce and heat through.
Add the egg (beat it before adding other ingredients), ricotta, 1 cup of the parmesan, 1.5 cups of the mozzarella (we are saving some mozzarella and parmesan to top the lasagna with), the Italian seasoning, garlic powder, and some salt & pepper to a bowl and combine until smooth.
Once the eggplant is done sweating, pat it dry with paper towels. Brush each piece with olive oil on both sides. Roast for 20 minutes.
Add a layer of the marinara sauce/beef to the bottom of a greased 9x13 baking dish, followed by a layer of eggplant (it's ok if it overlaps a little). Then, add the ricotta cheese layer, more eggplant, another ricotta layer, a marinara layer, and then the rest of the parmesan and mozzarella cheeses sprinkled over top. Lower the oven heat to 350F and bake uncovered for 30 minutes. Finish it off by broiling for 5 minutes or until the cheese is nicely browned.
Let the lasagna sit for 10 minutes prior to serving.
Serves at least 6 or more depending on how much people eat.
Inactive time represents the time the eggplant is being "sweated" and the time the lasagna is resting after it's cooked.
The jar of marinara I used for this recipe was 22 ounces, but anything in that range is fine (a bit smaller is ok).
If you have larger eggplants/more slices, feel free to build another layer vs. following exactly how I layered it.