Heat a couple of tablespoons of olive oil in your largest, heaviest skillet, cast iron is best, over medium high heat. Saute onions and peppers, together or separately depending on the size of your skillet, until they are softened and just beginning to caramelize. Remove to a large pan or pyrex dish and let cool while you cook the chicken.

Add a bit more oil to the pan and cook the chicken in batches, until golden brown on both sides and just cooked through. I like to use an instant read meat thermometer to eliminate the guess work and I pull them off the heat between 150 and 160 degrees. Pile the chicken breasts, as they are cooked, on top of the vegetables and when they are all finished, let cool then cover tightly with plastic wrap and refrigerate.

Early on the day you plan to serve the fajitas, slice the chicken into pieces, 1/3 to 1/2 inch thick then return them to the vegetables and toss to combine all, making sure to coat the chicken with the wonderful juices that will have settled to the bottom of the vegetables overnight. Cover tightly with foil and return to the refrigerator until you are about an hour away from service. It will take 45 minutes to an hour to warm the chicken mixture slowly, and tightly covered, in a 325 degree oven.

Serve with warm flour tortillas, sour cream, salsa, lettuce, shredded cheddar cheese, avocados and any other condiments you might like to add.