Prepare the Chicken - Cut each chicken breast in half horizontally lengthwise to make 2 thinner cutlets, 4 total.
Make the Marinade - In a medium bowl, whisk together the hot sauce, olive oil, salt, and black pepper—Reserve ¼ cup for topping the salad.
Marinate the Chicken - Add the chicken to a baking dish or large resealable plastic bag. Add the remaining buffalo sauce marinade, and turn to coat. Cover and refrigerate. Press out the excess air if using a plastic bag. Marinate for a minimum of 30 minutes and up to 60 minutes.
Cook the Chicken - Heat a large cast iron skillet or grill pan over medium heat. Add 1 tablespoon olive oil, and heat until hot and shimmering but not smoking. Shake off the excess marinade from the chicken, then add it to the pan and cook until golden brown, about 5 to 7 minutes per side.Cook until the internal temperature reaches 160 to 165ºF (71 to 74ºC) on a meat thermometer. Transfer to a clean plate to rest for 10 minutes.
Slice the Chicken - After resting, slice the meat against the grain. If desired, chop into cubes. Set aside or refrigerate until ready to serve.
Make the Dressing - In a medium bowl, combine ranch dressing, 2 tablespoons hot sauce, and cayenne pepper (if using)—season to taste.
Dress the Salad - Add romaine lettuce to a large bowl and ¼ cup of spicy ranch dressing. Gently toss to combine.
Add the Toppings - Top the lettuce with carrots, celery, tomatoes, cucumber, avocado, blue cheese, and onions. Serve with remaining ranch dressing and buffalo sauce marinade on the side.
Notes
Dressing Yield: About 1 cup
Storing: The undressed salad and dressing can be covered and stored separately in the refrigerator for up to 3 days.
Grilled Chicken: Preheat the grill over medium-high heat between 375 to 400ºF (191 to 204ºC). Clean and grease the grates with oil. Keep one burner off for indirect heat cooking. Place the chicken on the direct heat side and close the lid. Cook each side for about 5 to 7 minutes until the internal temperature reaches 160 to 165ºF (71 to 74ºC). If browning too quickly, move to the indirect heat side to complete.
Using Pre-Cooked Chicken: 2 ½ cups of shredded, sliced, or cubed chicken.