Slice the boneless thigh meat into 1/4 inch wide strips. Place them into a zip-lock bag - along with the chile/cumin/coriander/oregano, garlic paste and salt to taste. Pour in the vinegar and massage the bag until well combined. Marinate the mixture in the refrigerator overnight.
Slice the onion thinly. In a wok - over a high flame, add the chicken strips and sliced onions. With a wooden Wok Chuan (spatula), chop and turn the chicken/onion mixture until it is cooked - thoroughly. Serve in pre-warmed tortillas, topped with salsa or hot sauce.