Heat olive oil in a skillet over medium heat. Season the chicken with salt and pepper, then cook for about 6–7 minutes per side until fully cooked.
Brush the chicken with barbecue sauce during the last few minutes so it caramelizes slightly. Let it rest before slicing into bite-sized pieces.
In a blender, combine mayonnaise, sour cream, cilantro, garlic, lime juice, buttermilk, salt, and pepper. Blend until smooth and creamy.
Taste and adjust seasoning if needed. Chill the dressing for at least 10 minutes to allow the flavors to meld.
Finely chop the romaine lettuce into small pieces for that classic chopped salad texture. Halve the cherry tomatoes and dice the red onion.
Drain and rinse the black beans, and prepare the corn. Having everything evenly sized ensures each bite is balanced.
In a large bowl, combine lettuce, tomatoes, black beans, corn, red onion, and cheddar cheese. Toss gently to mix.
Top with sliced BBQ chicken and drizzle generously with cilantro ranch dressing.
Sprinkle tortilla strips on top just before serving. Toss lightly if desired or serve layered for presentation.
Serve immediately while the chicken is warm and the vegetables are crisp.