1Heat oven to 400°F. In medium bowl, stir Bisquick mix, garlic powder and water until soft dough forms. Let stand about 10 minutes or until cool.
2Meanwhile, in small bowl, mix mayonnaise, Cheddar and mozzarella cheeses, and onions until blended.
3Place dough on surface sprinkled with Bisquick mix; roll in Bisquick mix to coat. Shape into a ball; knead 12 to 15 times or until smooth. Press or roll dough until 1/8 inch thick. Cut with 2-inch round cutter dipped in Bisquick mix. On ungreased cookie sheet, place rounds about 1 inch apart. Spoon cheese mixture on each round.
4Bake 12 to 15 minutes or until topping is golden brown. Immediately remove from cookie sheet. Serve warm.