Chop onion and cilantro and prepare cheeses (if you need to grate them).
Add the olive oil, onion, chicken, salt & pepper, and BBQ sauce to the skillet on medium-high heat. Cook for five minutes, stirring occasionally, until it's all mixed together and starts bubbling.
Remove the chicken mixture from the pan and set aside.
Add a fairly even layer (some overlap is ok) of tortilla chips to the bottom of the pan. Add half the chicken mixture, followed by half the cheese. Add another layer of tortilla chips, the rest of the chicken mixture, and the rest of the cheese. Bake for 15 minutes.
Serve with cilantro sprinkled on top and a dollop of sour cream. Dive in immediately.
*I bought a 10.7 ounce bag of tortilla chips and ended up using about 3/4 of it. How many chips you use will really depend on the size of your pan and how much you layer them.