Cut the chicken into strips and place them in a bowl. Add 2 tablespoons of olive oil, lime juice, and the fajitas spice mix. Mix well and, if possible, let the chicken marinate for 30 minutes.
Heat a large non-stick pan and add 1 tablespoon of olive oil. When hot, add the chicken and cook for about 6-8 minutes, stirring occasionally to ensure even browning. Remove the chicken and keep it warm.
Add the remaining tablespoon of olive oil to the pan. Add the sliced peppers, sprinkle with salt, and add the onion. Sauté until the vegetables are soft, stirring occasionally. Return the chicken to the pan and stir to combine.
To prepare the guacamole, place the diced avocado in a bowl and mash with a fork. Add the remaining guacamole ingredients and mix well.
Warm the tortillas slightly. Take a tortilla and spread sour cream on the base. Add guacamole, then top with the chicken and pepper mixture. Sprinkle with grated cheddar cheese, fold the tortilla, and serve with extra sour cream, guacamole, and cheddar cheese on the side.