Peel, quarter and thinly slice onion. Coarsely chop mushrooms. In a bowl, combine flours, turmeric, chili powder, cumin, coriander and salt. Stir in onion, mushrooms and yogurt; mix well. Half fill a deep-fat fryer or saucepan with oil; heat to 375F. (190C.) or until a 1/2" cube of day-old bread browns in 40 seconds. Divide mixture in 10 equal portions. Drop spoonfuls of mixture into hot oil and fry 3-4 minutes or until golden brown and cooked through. Drain on paper towels. Garnish with parsley sprig, if desired, and serve warm.