I love, love, love this recipe! It uses ingredients I have on hand all the time, except the cilantro. In a pinch, I leave the cilantro out. If you are using frozen chicken, just throw it into a pot and boil the breasts until done - you can even over-cook them at this process to tender them up. Once cooked, drain the water and remove chicken. Shred or dice chicken, then return to the same pot with onions and continue recipe from there (no need to add olive oil if you do it this way).
By the way, I was bummed I wasted the chipotles so many times, so I discovered you can used dried chipotle powder instead and it is just as good!