Preheat oven to 400 degrees F (200 degrees C). Arrange oven racks so you have one low and one high in the oven.
Cut a shallow slit along the side of the eggplant and place into a baking dish.
Roast in preheated oven on the lower rack until the eggplant is completely shrunken and soft, about 40 minutes. Move dish to higher rack and continue baking until the skin is charred, about 5 minutes more. Let eggplant cool until cool enough to handle.
Peel and discard skin from eggplant. Put eggplant into a bowl; add tahini, garlic, lemon juice, red pepper flakes, and salt. Stir until ingredients are evenly mixed. Drizzle olive oil over the baba ghanoush and garnish with parsley.