Put the gram flour, salt, baking powder, cumin and chilli powder into a bowl and mix it well. Add water slowly to form a batter. Stir in crushed garlic and chopped onions into the batter and keep the mixture aside for 10 minutes.
Heat oil in a pan. Dip the mushrooms in the batter. Fry the coated mushrooms in the hot oil for about 2 minutes or until golden brown. Drain oil by keeping in paper towels. Serve hot.