Cook the pasta according to package directions for al-dente. Strain, rinse in cold water and set aside.

For the dressing, combine sour cream, mayonnaise, buttermilk and cider vinegar in a small bowl. Add crumbled gorgonzola and use a fork to mix in, smashing some against the side of the bowl to combine, but leaving some small chunks. Stir in the basil and salt and pepper to taste.

Toss the pasta with the red onion and about half of the dressing until all is well coated. Add the bacon, tomatoes, and steak and toss to combine, adding more dressing as desired. Top with avocado slices if using and server immediately.