Preheat oven to 400°. Cut eggplant crosswise into 1-in. slices; place on a greased 15x10x1-in. baking pan. Top with onion and garlic cloves. Drizzle with oil., Roast until eggplant is very soft, 40-45 minutes, turning and stirring vegetables once. Cool slightly., Place eggplant mixture in a food processor; process until blended. Transfer to a large bowl; stir in sour cream, lemon juice, salt, pepper and, if desired, liquid smoke., Sprinkle with parsley. Serve with flatbread and vegetables as desired.