If not already done, shred the rotisserie chicken and let it cool to room temperature before assembling the salad.
Remove any large stems from the romaine and coarsely chop or roughly chop the lettuce; place it in a large bowl.
Add the shredded chicken, 1/2 teaspoon garlic salt, drained corn, rinsed and drained black beans, diced red bell pepper, chopped Roma tomato, shredded Colby Jack, and chopped avocado to the bowl with the lettuce.
Use salad tongs to gently toss the salad components until evenly combined.
In a small mixing bowl, whisk together 1/4 cup barbecue sauce and 3/4 cup ranch dressing until smooth.
Portion the salad onto individual plates with tongs, drizzle the barbecue-ranch dressing over each portion, and sprinkle the crushed Doritos on top just before serving.