In a medium mixing bowl, combine the lemon juice, mayonnaise, buttermilk, sour cream, garlic powder and onion powder. Whisk the mixture together until smooth. Add the cheese and mix just until blended. Chill in an airtight container in the refrigerator at least 2 hours before serving.
Core and quarter each head of lettuce. Serve a generous dollop of dressing over each lettuce wedge and top with the bacon and tomato. Season with pepper.