While it might seem like a quick and easy way to make a meal, those pre-formed, crunchy taco shells that you can buy off the shelf are a travesty to authentic Mexican food.  They are basically a taco-shaped chip and are laden with fat, calories and processed corn.  Real corn tortillas are made from masa, which is very different from ground corn, and can be quickly steamed for a healthy and delicious taco shell.  If crunchy is what you crave, just cook the tortilla in a bit of hot oil until it begins to crisp up, and fold it in half while it cools on paper towels.