1Heat oven to 400°F. In 9-inch cast-iron skillet, cook bacon until crisp; drain on paper towels. Crumble bacon; set aside. Reserve 2 tablespoons bacon drippings in skillet, coating bottom and side completely. Discard any remaining drippings.
2In large bowl, stir Bisquick mix, milk, 1/4 cup of the onions, the garlic powder and red pepper until soft dough forms. On surface sprinkled with additional Bisquick mix, pat dough to 1-inch thickness. Cut dough with 2 1/2-inch round cutter. Arrange rounds in skillet; sprinkle 3/4 cup of the Cheddar cheese evenly between rounds.
3Bake 15 to 17 minutes or until lightly browned. Sprinkle mozzarella cheese and remaining 3/4 cup Cheddar cheese on tops of biscuits. Bake 2 to 4 minutes longer or until cheese is melted. Sprinkle with bacon and remaining 2 tablespoons onions. Serve warm.