Cut chicken breasts into bite sized pieces; place in sealable plastic bag.
Whisk fajita seasoning into the chicken broth; pour over chicken in plastic bag; shake well and seal tightly , place in fridge to marinate for 30 minutes or more.
Veggie spray non stick wok or large frypan; heat to medium hot; pour chicken with marinade into wok, stir fry and cook down to about 1/4 cup of mainade. about 10 minutes.
Add sweet peppers and red onion to wok, add salt and pepper, stir fry until almost all of the marinade is gone, (or until the consistancey you prefer), about 10 minutes; we like our veggies tender crisp).