Cumin normally forms a big part of Mexican recipes that I've seen and tried so would definitely have that in there.
Something like, Cumin, Smoked Paprika, a herb of some sort, probably Oregano, Onion powder, Garlic powder, some sort of chilli (Chipotle is my personal preference however not sure if that's authentic, could always substitute for a normal chilli powder), maybe a bit of Cayenne and finally salt and pepper.