Bring a large pot of water to a boil. Salt the water and stir in the pasta. Cook until al dente. Rinse with cold water and set aside.
While the pasta is cooking, make the Creamy Avocado Dressing. Combine all of the dressing ingredients in a blender or food processor and blend until smooth.
In a large bowl, combine pasta, black beans, tomatoes, peppers, red onion, corn, and chopped avocado. Pour dressing over pasta salad and stir until salad is well coated. Season with salt and pepper. Squeeze fresh lime juice over the salad, so the avocados don't brown. Garnish with chopped cilantro and serve at room temperature or chilled.
Note-you may have leftover dressing, depending on how "dressed" you like your pasta salad. If the dressing is too thick, add more buttermilk.