Mix together the chilli oil, paprika, chilli powder, sugar and the lime juice and zest. Cut each chicken breast lengthways into six strips. Add to the chilli paste, cover and leave to marinate for 1-2 hours.
Meanwhile make the tomato and avocado salsa. Place all the ingredients into a large bowl and stir gently to combine. Season with salt and pepper and place in a serving bowl.
Heat a barbecue or a ridged griddle pan.
Thread three pieces of chicken onto each skewer, place on the barbecue or griddle pan and cook for 3-4 minutes on each side until the chicken is cooked through.
Place the chicken skewers on a serving plate and hand around the tomato and avocado salsa, warmed tortillas, lettuce and soured cream and allow each person to assemble the fajitas themselves.