Preheat oven to 425 degrees. Pierce eggplant with tines of a fork and wrap tightly in foil. Place eggplant on baking sheet and roast for 1 hour. Cool slightly. Halve eggplant lengthwise and scoop out pulp into a medium bowl. Set aside and reserve.
Meanwhile, heat walnuts in a dry skillet over medium bowl. Set aside and reserve. Into bowl with eggplant, stir in walnuts, raisins, mint, lemon juice, garlic and oil. Season with salt and pepper. Cover and chill slightly.
Preheat broiler. sprinkle pitas with cheese, dividing equally. Broil for 2 minutes or until cheese melts and pitas are lightly toasted. Cut each pita into 6 wedges and serve with dip.