First, prepare your marinade according to the package directions. Our favorites are the Baja Citrus and the Caroline Country variety. Place the marinade and the chicken breasts into a large zippered plastic bag and marinate as long as possible, preferably overnight.
When you are ready, preheat your oven to 400 degrees (F). Then heat a large, heavy, ovenproof skillet (cast iron works great) over high heat on the stove. Remove the chicken breasts from the bag and put them into the skillet. Let them sear well on the first side without disturbing them. It will take about 7 minutes, depending on your skillet and heat. Once they have a nice caramel color, flip and sear the same on the other side. Once seared, place the chicken breasts to the side on a plate temporarily.
Toss the onion and bell pepper into the bag of remaining marinade, and pour all of it into the hot skillet. Saute the vegetables for about 5 minutes. Then remove the skillet off the heat. Add the chicken breasts back in, settling them down where the onion and bell pepper are surrounding them, but not underneath. Cover the whole pan with a lid (if you have an oven proof one) or foil. Then put it in the oven. Bake until chicken is cooked thru, about 30 minutes.