Meanwhile in small bowl mash beans with fork, stir in reserved bean liquid and chili powder, mix well. Spread evenly over baked crust. Top with mushrooms, tomatoes and jalapeno pepper slices. Sprinkle with cheese. Bake at 200ºC or 5 to 10 minutes or until cheese melts. Cut squares and top each with sour cream, green onions and sliced olives. Serves 6 or makes dozen appetizers. Enjoy