In a plastic bag, combine 2 tablespoons of cooking oil, garlic, ground cilantro, ground cumin, ground cayenne pepper, dried oregano, and kosher salt to create a marinade.
Place the 4 boneless, skinless chicken breasts into the bag, ensuring they’re fully coated with the marinade. Let the chicken marinate in the fridge for at least 20 to 30 minutes.
Heat the remaining 1 tablespoon of cooking oil in a cast iron skillet over medium-high heat.
Add the sliced onions and sliced bell peppers to the skillet. Cook for about 7 to 10 minutes, stirring occasionally, until softened and browned.
Once cooked, remove the vegetables from the skillet and set aside. Add the marinated chicken to the skillet and pan-fry for about 5 to 7 minutes on each side, until golden brown and cooked through.
Remove the chicken from the skillet and let it rest for about 5 minutes before slicing into strips.
Return the cooked vegetables to the skillet to re-warm, then add the sliced chicken back into the skillet and stir to combine. Season with fresh lime juice if desired.
Serve the chicken and vegetable mixture with warmed flour tortillas for everyone to assemble their own fajitas.
