Toss the chicken, bell pepper and onion in the mixture of the taco seasoning and oil, place in a single layer on a baking sheet and bake in a preheated 400F/200C oven until the chicken has cooked though, about 15-20 minutes.
Slice the chicken.
For the fajitas:
Assemble the fajitas as desired and enjoy!
For the nachos:
Spread the tortilla chips over the baking sheet, top with the chicken, peppers and onions followed by the cheese and bake in a preheated 400F/200C oven until the cheese has melted, about 5 minutes.
Top with pico de gallo, guacamole, sour cream and cilantro and enjoy.