In a large bowl, combine chicken, 1 tablespoon vegetable oil, BBQ seasoning, 1/2 teaspoon salt and 1/4 teaspoon pepper.
Heat remaining 1 tablespoon vegetable oil in a cast iron grill pan over medium-high heat. Working in batches, add chicken to the grill pan in a single layer and cook until golden brown and cooked through, reaching an internal temperature of 165 degrees F, about 6-8 minutes. Set aside and stir in BBQ sauce until well combined.
Add corn to the grill pan, and cook, turning occasionally, until charred and tender, about 5-10 minutes; let cool before cutting the corn kernels off the cobs.
To assemble the salad, place romaine lettuce in a large bowl; top with chicken, corn, tomatoes, black beans, avocado, red onion and cheese. Pour the ranch dressing on top of the salad and gently toss to combine.