Wash hands with soap and water for 20 seconds.
Place chicken breasts in a gallon size plastic bag and, using a meat tenderizer, pound the chicken breasts until they are thin.
Sprinkle 1/8 teaspoon of salt over each chicken breast. Place them in the fridge for 30 minutes.
Wash the counter and utensils that touched the raw chicken. Wash hands with soap and water after handling raw chicken.
Scrub the onion with a clean vegetable brush under cold running water. Gently rub pepper under cold running water.
In the meantime, slice bell peppers and onions. Set aside.
In a small bowl, combine chili, cumin, garlic, onion, paprika, black pepper, and cayenne. Mix, then set seasoning aside.
In another bowl, combine diced onions and chopped cilantro. Mix and place in fridge.
After thirty minutes, get chicken out of the fridge and pat it dry. Preheat a skillet over medium heat.
Season chicken breasts on both sides with 2/3of the seasoning mix.
Add oil to skillet, then add chicken breasts. Cook one side for 8 minutes, then other side for 4 minutes. The chicken is done when the internal temperature reaches 165°F.
Wash the counter and utensils that touched the raw chicken. Wash hands with soap and water after handling raw chicken.
Remove chicken from skillet and set aside.
Take a paper towel and wipe off most of the oil from the skillet. Leave just a bit of oil in the skillet to cook vegetables.
Return skillet to stove, add onions, and cook for about 10 minutes.
While onions cook, slice chicken breasts into cubes. Set aside.
Once onions start to caramelize, add bell peppers and rest of the seasoning mix, and cook for another 10 minutes.
While fajita veggies continue to cook, warm up tortillas if desired in a separate skillet. Set aside.
When veggies are cooked, turn off heat and begin assembling fajitas. In tortillas, add a layer of chicken, fajita veggies, and onion/cilantro mix. Add a squeeze of lime over fajitas before eating.