In a small mixing bowl, combine the sour cream or Greek yogurt, lime juice, olive oil, cumin, chili powder, and a pinch of salt and pepper. Whisk until smooth and creamy. Set aside.

In a large mixing bowl, add the chopped cooked chicken, rinsed black beans, sweet corn, diced red bell pepper, and finely chopped red onion. Gently fold in the halved cherry tomatoes and the diced avocado. Sprinkle the cilantro over the top and combine thoroughly.

Pour the dressing over the salad mixture and gently toss everything together until all ingredients are well coated.

Transfer the salad to a serving dish. Top with shredded cheese and optional tortilla strips or chips. Chill in the refrigerator for at least 30 minutes before serving.