For the dipping sauce, combine all the ingredients and refrigerate for at least 30 minutes.
For the mushrooms, mix the flour, baking powder, water and tandoori marinade in a small bowl. Place the bread crumbs in another small bowl. Dip the mushrooms, one at a time, into the tandoori mixture, then dip them into the bread crumbs, turning to coat evenly. Set aside on a plate and repeat the process with all the mushrooms.
Heat 2 to 3 inches of oil in a deep fryer or heavy saucepan to 375 degrees. Fry a few mushrooms at a time, 1½ to 2 minutes, or until deep golden brown, turning over several times. Do not exceed 2 minutes or the mushrooms will release too much liquid, preventing your fried mushrooms from being crispy.
Remove mushrooms from the oil and set on paper towels to drain. Serve immediately with the dipping sauce.