BBQ Chicken Salad

Name: BBQ Chicken Salad
Ingredients: 2 boneless, skinless chicken breasts (about 1 lb. total); 0.75 c. store-bought BBQ sauce, divided; 0.333 c. buttermilk; 0.25 c. mayonnaise; 0.25 c. sour cream; 1 clove garlic, finely chopped; 2 tbsp. chopped fresh parsley; 1 tbsp. chopped fresh dill; 1 tbsp. sliced fresh chives; 0.25 tsp. onion powder; 2 heads romaine lettuce, thinly sliced (about 8 c.); 1 (15-oz.) can black beans, rinsed, drained; 1 vine-ripened tomato, finely chopped (about 1 c.); 1 c. shredded Mexican blend cheese; 1 c. frozen corn, thawed, drained; 1 c. tortilla strips or crushed tortilla chips; 0.25 c. finely chopped red onion