If you are fortunate enough to have pork belly (you could always use left over roast or pulled pork) put a little oil in skillet and brown it until crispy.
Take your warmed tortilla, add a big spoon full of crispy pork belly (or other meats), sprinkle with the onion, cilantro, green sauce and a small handful of queso fresco. You can add tomato if you so desire.