Preheat a grill to medium-high heat. Brush both sides of the pounded chicken breast with olive oil and sprinkle with salt and pepper. Grill on one side for 4 minutes, flip, brush the grilled sides with barbecue sauce, then grill the other side for 3 to 4 minutes, until the chicken is cooked through. Remove to a serving plate and brush the other grilled side with barbecue sauce. Cover and let rest for 5 minutes, then chop into bite-sized pieces.
Prepare the dressing: In a small bowl or measuring cup with a spout, stir together the ranch dressing and barbecue sauce. Taste and adjust the ratio as desired.
In a large serving bowl, combine the romaine, tomatoes, beans, Mexicorn, red onion, and chopped chicken. Drizzle the salad with dressing, then toss to lightly coat. Serve immediately, topped with crushed tortilla chips and cilantro.
TO STORE: Refrigerate leftover salad in an airtight storage container for up to 3 days.