You will need:
thin cut skillet steak (I usually get thin cut round eye)
fillings of your choosing such as cheese, lettuce, salsa, cholula hot sauce, guacamole, etc.
The steak is going to cook super fast on the stove top. Before you start cut your onion and pepper into strips. Heat your skillet over medium heat with a small amount of oil. Season your steaks with cilantro, salt and pepper. The steaks will cook in about 2 minutes per side. Take your steaks off the heat and cut into thin strips. Now saute your cut onions and peppers for your fajitas, do so now IN the pan you just cooked the steaks in - utilize all that flavor :)
Now you just need to build your fajitas and enjoy!