In a blender, combine the mayonnaise, sour cream, buttermilk, fresh cilantro, lime juice, garlic, ground cumin, and chili powder. Blend until smooth and refrigerate for 30 minutes.

Rinse and chop the romaine lettuce into bite-sized pieces. Drain and rinse black beans. Prepare corn as needed, and chop the bell peppers, onion, and tomatoes.

In a large mixing bowl, combine all chopped ingredients: romaine lettuce, black beans, corn, bell peppers, red onion, tomatoes, and avocado. Gently fold together.

Lightly toss the combined ingredients using two serving spoons to maintain their integrity.

Drizzle the chilled dressing over the salad mixture and toss lightly to coat. Add more dressing if desired.

Serve immediately for the best flavor or store salad and dressing separately until ready to serve.

Before serving, add toppings like tortilla strips, pickled jalapeños, and optional proteins.