Sure, fajitas are traditional for both Mexican and Tex-Mex. It's just grilled marinated skirt steak.
I love them but rarely order them out because they're so expensive. They used to be super-cheap because it's a tough, stringy cut of meat. It was poor-people food. It has to be marinated and/or mechanically tenderized to make it edible. Back in the 80s and even early 90s I could buy it for $.59/lb. Now I'm lucky if I can find it on special for $8 or $9 per lb and that's at the carnicerias, the gringo grocery stores are a couple bucks more. And ordering it already prepared at a restaurant? Might be paying upward of $30 or $40 per lb.
Oh and because we excel at pedantry around here, there is no such thing as a chicken fajita or a shrimp fajita or even a ribeye fajita. "Fajita" refers specifically to the cut of beef-- the skirt steak-- and not the preparation of tacos.
If you order a "chicken fajita" then you're actually eating tacos de pollo asado.
