In a large bowl, combine the flour, baking powder and sugar. In a small bowl, whisk milk and mayonnaise until smooth. Stir into the dry ingredients just until moistened. Fold in the bacon, tomatoes and parsley.
Fill 12 greased or paper-lined muffin cups two-thirds full. Bake at 400° for 20-25 minutes or until a toothpick inserted in the center of a muffin comes out clean. Cool for 5 minutes before removing from pan to a wire rack to cool completely. If desired, sprinkle with lettuce.