Preheat the oven to 400°F. Cut off the top and bottom of the eggplants. Slice the eggplants into vertical strips about 1/2 inch thick.
Oil a large baking sheet and place the eggplant slices on it. Brush them with olive oil, and sprinkle with salt. Bake for about 15-20 minutes, or until the slices are tender and golden.
Meanwhile, place a large skillet over medium-high heat. Add a tablespoon of olive oil, then add the chopped onion and sauté until it is softened. Add the garlic and cook for another minute.
Add the ground beef and season with salt. Cook until the beef is no longer pink.
Pour in the marinara sauce, reduce the heat to medium-low, and simmer for about 15-20 minutes.
To make the cheese sauce, mix together the ricotta cheese, egg, and 1 cup of mozzarella cheese in a medium bowl until well combined. Set aside.
Spread about 1 cup of the meat mixture in the bottom of a 9x13 inch baking dish. Top with a layer of eggplant slices.
Spread half of the cheese sauce evenly over the eggplant slices. Layer on another 1.5 cups of the meat mixture, then sprinkle 1.5 cups of the shredded mozzarella cheese on top.
Repeat the layers of eggplant, the remaining half of the cheese sauce, and the remaining meat mixture and mozzarella.
Bake the eggplant lasagna uncovered at 350°F for 25-30 minutes, or until the cheese is slightly golden and bubbly. Serve warm and enjoy!