Slice the onion, pepper, and chicken, and sauté it in oil with spices until cooked through.
If you are making the optional guacamole sauce (you can easily substitute with chopped, fresh avocado if you don't want to make sauce), place all those ingredients into a blender and blend until you have a smooth sauce. Use water to loosen the consistency into a true sauce.
Layer all the fajita ingredients onto your tortilla and roll it up tight.
Cut it in half.
Serve.
Video
Notes
Please note that the nutrition data given here is a ballpark figure. Exact data is not possible.