In a bowl, combine Red chilli powder, Cumin powder, pepper powder, lime juice, oil, salt; mix together. Add the chicken strips and If time allows, let marinate for 1 hour.
Heat a skillet or pan on medium-high heat until smoking. Add a drizzle of oil of your choice to lightly coat the bottom of the pan. Sear the chicken on both sides until golden.Flip them a couple of times while cooking so they get cooked evenly on both sides.
Transfer chicken to a plate, let it rest.
For the fajitas
Add the peppers and onions to the skillet and cook until the onion is soft and the peppers are slightly charred.
Spoon filling down the center of tortillas and top with chicken seasoned, lettuce, guacamole and sour cream.