Preheat oven to 425 degrees F.Trim the stem end off of the eggplant and cut the skin off, about 1/8" deep, along two opposite sides. Cut the eggplant into 4 planks, each about 1/2" thick. Place eggplant on sheet pan and lightly coat with olive oil spray on both sides. Season to taste with salt and pepper if desired. Roast for about 25 minutes, carefully turning once with a spatula midway through cooking. Remove and set aside on pan.
Place the ricotta cheese in a bowl and add the oregano, 1 tablespoon of the chopped basil, olive oil and garlic. Season with salt and pepper if desired and blend well.
Divide the ricotta between the four slices of eggplant and spread evenly. Top each with 1 ounce of the shredded mozzarella cheese and place back in the oven for about 5 to 10 minutes, or until the cheese is melted. When melted, remove from oven and top each with 1 whole basil leaf, divide the sauce between the four slices and sprinkle each with 1 teaspoon grated Parmesan cheese.
Return to bake an additional 5 to 10 minutes. Garnish with shredded basil before serving.