Mix the first 6 ingredients in a large zip-close bag.
Add chicken, pepper strips, and onions to the marinade in the bag. Seal and mix ingredients together until all of the chicken and vegetables are coated with the marinade.
Refrigerate 15 minutes.
Spray a grill pan with cooking spray and heat to medium-high heat. Transfer 1/2 of the contents from the bag onto the grill pan, as to not overcrowd the grill pan. Grill 8-10 minutes, or until chicken is fully cooked, vegetables are crisp-tender, and there are visible grill marks. Drain the liquid from the grill pan and repeat with the other 1/2 of the contents in the bag.
(If you don't have a grill pan, use a skillet and drain the liquid once the food is cooked. Then allow it to cook a little longer in the skillet at medium-high heat so the chicken and vegetables can lightly brown in the pan.)
Scoop 2/3 cup chicken/vegetable mix onto each tortilla. If desired, scoop 2 tablespoons sour cream on top of each and serve.