Preheat the oven to 350°F (175°C).
Slice the eggplants into about 1/4" thick strips. Arrange on a baking sheet, brush both sides with olive oil, and season with sea salt and black pepper.
Roast the eggplant in the preheated oven until tender, about 10 minutes.
If using ground beef, cook it in a skillet until browned, drain excess fat, and stir into the marinara sauce.
In a mixing bowl, combine the ricotta, eggs, and grated Parmesan until smooth.
Prepare a 9x13-inch baking dish with nonstick spray or a light coating of olive oil. Layer the lasagna starting with a thin layer of marinara, half of the ricotta mixture, a single layer of roasted eggplant, the remaining ricotta mixture, more marinara, and finish with the grated mozzarella on top.
Bake the assembled lasagna in the oven until the cheese is melted and the dish is bubbly, about 30 minutes.
Let the lasagna rest for 5–10 minutes before slicing and serving.