Heat the oil in a skillet and add the potatoes.

Saute in the oil, stirring often, for 5 minutes or until browned on the bottoms.

Add half the water and bring to a boil.

Turn the heat down and simmer, covered, for a few minutes until the potatoes are cooked through.

Take off the lid and simmer them for 1 minute more.

Add the beef, garlic, cumin, oregano, salt, and black pepper.

Cook for a few minutes until the beef is cooked through.

Add the remaining water and boil for 2 minutes.

Take the pan off the heat.

Warm the taco shells in the microwave for 45 seconds.

Divide the beef mixture between the warmed taco shells.

Top with the lettuce, tomatoes, cheese, cilantro and sour cream, and serve immediately.