Preheat the grill or oven to 400ºF.
Prepare the peppers and onions by slicing them into 1-inch squares. Transfer them into a gallon-sized bag and add a tablespoon of olive oil. Shake to coat everything in oil.
Prepare chicken breast by slicing it into 1-inch by 1-inch chunks (make sure they're all around the same size) and then transfer them into another gallon-sized bag.
In a small bowl, combine the fajita spices to create your rub.
Add half of the spice mixture to the vegetables and the other half to the chicken. Shake well and let sit for 10 minutes.
Now, make your kababs. Alternate between peppers, onions, and chicken until you've filled all your skewers.
Lay a piece of tin foil onto the grill and spray it with cooking spray.
Grill the chicken kababs over direct heat for around 15 minutes, rotating every 4-5 minutes. Cook until the internal temperature of the chicken is 165ºF.
Remove from heat and squeeze on lime juice (THIS PART IS KEY) and sprinkle on fresh cilantro. Enjoy!