Spread half of the BBQ sauce over the bottom of a small slow cooker, Arrange chicken breasts in a single layer in the bottom of the crock pot and top with remaining BBQ sauce. Cook on low 4-6 hours or until chicken easily shreds.
To make the dressing, combine the ranch, buttermilk, lime juice, and cilantro in a small food processor or blender; mix until smooth. Set aside.
In a large bowl, combine the mixed greens, corn, and black beans. Drizzle dressing over the salad and toss well. Distribute the salad among 4 plates and top with 4 ounces chicken, ¼ avocado, and ½ ounce chips. Serve immediately.