Preheat oven to 425°F. Melt butter in a skillet over medium high heat. Add the mushrooms and sauté until they are soft and all liquid is evaporated. Transfer to a bowl to cool and set aside.
Slice pitas into 8 wedges each and transfer to a baking sheet. Brush with olive oil and toast in the oven until crisp, about 15 minutes. Add the remaining ingredients to the cooled mushrooms and mix well. Serve with toasted pita wedges.
Makes 2 cups.