Cut the chicken breasts into long strips; set aside. Slice the onion into long strips. Slice the peppers into long ¼ inch strips.
Heat the olive in a large skillet. Add the chicken to the skillet then sprinkle about half of the fajita seasoning over the chicken and toss. Cook the chicken for 5 to 10 minutes until it's fully cooked and no longer pink, and it's slightly charred, but not burned. Transfer the chicken to a plate and set aside.
Add another tbsp of olive oil to the skillet, if needed. I used a non stick skillet, so it wasn't necessary to add anymore oil. Add the onion and cook for a couple minutes until it's slightly translucent. Add the peppers and the remaining fajita seasoning and toss. Cook for another 3 to 5 more minutes so the peppers cook slightly, you don't want them over cooked, they should be a bit crunchy. Add the chicken back to the skillet and toss with the peppers.
Serve over tortillas and top with salsa, sour cream and any of your favorite toppings.
If you can't find fajita seasoning, try my Fajita Seasoning recipe. A pre-made fajita sauce will also work.