Bring a large pot of salted water to a boil. Cook pasta according to package directions, about 12-13 minutes. Drain and rinse with cool water. Set aside.
To make the dressing, in a medium bowl, whisk to combine mayonnaise, buttermilk, ranch seasoning mix and 2 tablespoons parsley. Set aside.
In a large bowl, toss to combine tomatoes, lettuce, 3/4 of the cooked bacon, scallions, salt and pepper. Drizzle in 1/4 cup dressing and toss to coat. Use a small spoon and fill the shells with the salad.
To garnish, drizzle the dressing over the shells and top with 1 tablespoon chopped parsley and remaining chopped bacon.