Add all of the chicken marinade ingredients into a gallon sized zippered bag. Smush around to make sure the chicken is thoroughly coated. Squeeze all air out of bag and seal. Place in refrigerator for at least 1 hour (4 hours is better) up to overnight.
In a large saute pan over medium high heat, add chicken breasts (along with marinade). Cook for 4 minutes on each side. Then reduce heat to medium and cover pan. Allow to cook another 10 minutes. Confirm internal temperature has reached 165degF and remove to cutting board. Let rest while you build taco, before slicing.
In a small frying pan over medium high heat, lightly toast each tortillas (about one minute on each side).
Smear half of tortilla with sour cream. Drizzle with taco sauce and sprinkle with cheese. On the other half add lettuce, tomato and onion.
Slice chicken into ¼ inch pieces and add a portion to each taco.