Heat a saute pan or a wok (I find the high walls of a wok to work very well for fajita cooking) over medium-high heat. Add in cooking oil and then chicken to heated oil and saute until golden on the outside, ~3 minutes. Use tongs to remove chicken from pan, leaving oil (and all those yummy spices) in the pan. Set chicken aside (does not have to be cooked through at this point).
Add onions to the pan and saute until softened and translucent, ~3 minutes. Toss in zucchini and saute for ~2 minutes before adding in peppers and garlic. Cook for another 3 minutes. Add chicken (and all its juices) back into the pan. Toss through and cook until chicken is done (you might just have to slice through to check).
Remove from heat and finish with lime juice. Toss with cilantro and season to taste with salt, pepper, and / or hot sauce. Enjoy!