Pour lemon juice over the avocado slices and set aside. Place chopped romaine in a large bowl and toss with enough blue cheese dressing to lightly coat, about 1/3 cup. Set aside remaining dressing for another use.
To assemble salads, place the ring mold on a chilled serving plate and fill with 1 cup of the romaine mixture, making sure that the lettuce fills the whole diameter of the bottom circumference. Carefully place 2 avocado slices on top of the lettuce on the right side of the mold, so that their curvature aligns with the mold. On the opposite side of the avocado, sprinkle corn on top of the lettuce so that it extends 1 1/2 inches from the left side of the mold. Next to the corn, sprinkle a 1/2-inch thick row of diced tomatoes. Next to the tomatoes and meeting the avocado, sprinkle a row of crumbled bacon. Garnish with a very thin row of blue cheese crumbles down the center. Carefully remove the mold by lifting straight up (some ingredients will shift). Repeat with remaining ingredients. Serve immediately.
Cook's Note: If a ring mold is unavailable, use a 12-ounce tuna can (4-inch diameter by 2-inch height) and remove the top and bottom with a can opener.
Blue Cheese Dressing:
In a medium bowl, mix the mayonnaise, buttermilk, lemon juice, salt, and cumin until smooth. Fold in the crumbled blue cheese and chives. Refrigerate until ready to use.