Slice the chicken breasts into thin strips, about 1" thick.
Slice the onions & peppers lengthwise, about 1" strips.
Combine all Fajita seasoning ingredients.
Heat a large frying pan with oil. Add chicken and cook until no longer pink, about 6 minutes.
Add the fajita seasoning and 1 c. water, mixing well. Continue to cook another 4 minutes.
Add the onions & peppers and cook until onions become translucent, stirring occasionally, for about 5 minutes.
Warm the tortilla shells according to package instruction.
Assemble fajitas with the chicken fajita mix, sour cream and other toppings to your liking, folding into a tortilla shell.