Combine chicken and BBQ sauce in a large bowl or gallon-sized plastic bag; gently toss to coat. Set aside to let marinate for at least 20 minutes at room temperature, or cover and refrigerate for 4-8 hours (or 1-2 days in advance), if desired.

Preheat grill to medium-high (350-400 degrees F). Meanwhile, thread chicken onto pre-soaked skewers.

Once the grill is hot, add chicken and cook for 3-4 minutes before turning. Baste chicken with any reserved BBQ sauce from the marinading process. Cook chicken until fully cooked through, totaling 15-18 minutes. During the chicken cook time, add the corn on a top grate or away from direct flame; turn every 2 minutes, cooking a total of 10-12 minutes.

Remove corn and chicken from grill and set aside. After cooling for 5 minutes, cut corn from cob.

Combine ranch, BBQ sauce, and buttermilk in a mason jar or small bowl, whisking or shaking until well-combined.

Place romaine in a large bowl and add most of the dressing; toss to coat. Add tomatoes, beans, and avocado along with remaining dressing; toss and serve with skewers atop the salad.