Preheat the oven to 375 degrees F.
In a large bowl, mix together the ground beef, basil, Parmesan, tomato-basil sauce, breadcrumbs, salt, pepper, garlic, eggs and onions until combined. Press the mixture onto the bottom of a nonstick baking sheet. Bake until cooked through or when an instant read thermometer registers 160 degrees F when inserted into the meatloaf, 20 to 25 minutes.
In a large skillet, heat the oil over medium-high heat. In batches, add the eggplant slices and cook until lightly browned, 2 to 3 minutes. Turn the slices over and season with the salt and pepper. Cook for 2 to 3 minutes longer.
Arrange the eggplant slices on top of the meatloaf in a single layer. Spoon 1 to 1 1/2 tablespoons of the tomato-basil sauce into the center of each eggplant slice. Top with the mozzarella and bake until the cheese is just melted, an additional 5 minutes.
Cut into 6 to 8 squares and serve with additional tomato-basil sauce.