1. Preheat grill to medium-high. Brush chicken all over with oil; season with salt and pepper. Oil grill. Grill chicken until cooked through, turning once, about 10 minutes total. Cut chicken into small cubes and refrigerate.
2. Brush corn with butter. Oil grill. Grill corn, turning occasionally, until just tender and slightly charred on all sides, 8 to 10 minutes total. Transfer corn to a cutting board to cool. When corn is cool enough to handle, use a sharp knife to carefully slice kernels off cob. Discard cob. Place kernels in a large bowl and refrigerate.
3. Blend mayonnaise, buttermilk, chipotle, adobo, cumin, cilantro, lime juice and 1/4 tsp. salt in a blender or food processor until smooth.
4. Place lettuce, chicken, tomatoes, avocado, onion and black beans in bowl with corn. Add dressing to taste and gently toss to coat. Season with salt and pepper. Top with chips and serve immediately.