Cut the romaine lettuce heart in half lengthwise. place the romaine halves on a cutting board, flat-side down, and cut into half lengthwise again. cut each quarter into 4 (2-inch) pieces to create 16 "cubes".
Stir together the mayonnaise, buttermilk, lemon juice, pepper, salt, and half of he blue cheese in a small bowl.
Alternatively thread the romaine cubes, cherry tomatoes, and red onions evenly onto 8 (6-inch) skewers. Place the skewers on a platter. Drizzle with the dressing. Sprinkle withthe bacon crumbles and remaining blue cheese.