Slice Chicken very thinly (you want thin bite-sized pieces). Then sprinkle the chicken with Cayenne pepper and set aside.
Cut all the Bell Peppers, Onion, lime, cilantro. I will usually cut all of my toppings (Avocados, jalapeños, and etc.) at this time as well.
Heat up 3 Tablespoons of Olive Oil in your Cast iron skillet (you could use a wok or a non-stick pan but the iron skillet produces the best results). Place the chicken in the pan snd spread around the pan to make an even layer. You want a good sear on the chicken. Add spices to chicken including just 1 tsp of Salt. Use tongs to flip the chicken pieces. And watch out for splatter. Cook until chicken looks like it has a good sear (2-3 minutes or so) and almost cooked through. Then add the lime juice from half of a lime. Cook 1 minute then remove chicken from pan with tongs and set aside. Make sure to keep remaining juices in the pan.
If you need, add one more Tbsp oil to your pan. Once the oil is heated, add the Onion and Bell Peppers. After 1-2 minutes put in Garlic. Cook for a few minutes allowing some of the veggies to get nice charred look. Then add the chicken again and mix the veggies with the chicken. Add the remaining lime juice and another ½ tsp of salt. Cook a couple more minutes and then keep the Fajita mixture on low while you warm your tortillas. Make sure to watch your chicken so it doesn't over cook! Use corn or flour tortillas and top with cilantro, salsa, black beans, sour cream, or avocados. Enjoy!