1. Place sliced onions in a heat-safe bowl. In a small pot, combine vinegar, water, sugar, and salt; bring to a gentle boil. Once the liquid starts bubbling, pour it over the onions. Let sit for at least 20 minutes (or ideally an hour).
2. Place each chicken between two pieces of plastic wrap and pound to 1/2” thick. Cut each in 2 smaller pieces, transfer to a bowl, and mix with the kosher salt and 1/4 cup of the BBQ sauce. Mix and marinate for at least 30 mins at room temp, or up to 12 hours in the fridge.
3. Make the dressing: In a medium glass measuring cup (or bowl), whisk together the light sour cream, BBQ sauce, mayonnaise, apple cider vinegar, water, sugar, salt, and pepper. Set aside.
4. In a large cast iron skillet or grill pan, heat the avocado oil over medium-high until shimmering. Add the chicken in a single layer, letting excess marinade drip off. Cook for about 5 mins per side, until browned with some char and the internal temperature reaches 165F.
5. Transfer the chicken to a cutting board and let rest for 5 minutes. Cut into bite-size cubes, then toss with the remaining 1/4 cup BBQ sauce in a medium bowl.
6. Assemble the salads with romaine on the bottom, and piles of BBQ chicken, cherry tomatoes, avocado, corn, cheddar cheese, tortilla chips, cilantro, and pickled onions on top. Drizzle on the dressing to taste, toss, and enjoy!
