Combine the marinade ingredients in a small bowl and set aside. Now, thinly slice about 4 boneless, skinless chicken breasts. They should be about 3/8 inch thick, or as thin as you can slice them.
(This made about 9 or 10 fajitas. In the future I will use more chicken for my bottomless pit husband and sons.)
Take the chicken and place it in a large zip-lock bag. Pour in the marinade and squish it all around. Set it in the fridge and let it get happy for at least an hour. I had a busy day that day, so I did this around 11. This makes a great week night meal because you can do this ahead of time.
When you are ready for dinner and the chicken is marinated…thinly slice the onion and pepper.
Set your oven on "Warm" or the lowest temperature and have an oven-safe dish handy.
In a skillet, sauté the onion and peppers in butter or olive oil (I prefer butter) until the onions are golden and they are tender. Place them in the dish and put them in your oven to stay warm.
Now, heat your skillet up over medium high heat.
Add some butter and begin cooking your chicken in batches.
The chicken will cook fast and you want it nice and browned/seared. Brown each side and place it in your dish in the oven.
Repeat until all the chicken is cooked, adding butter as needed. Serve these on tortillas with desired toppings.