In a heavy bottomed skilled heat oil on medium high heat. Add half of the diced onion and sauté until softened. Add ground beef and break up with a wooden spoon browning until cooked through. Add taco seasoning and stir until combined. Add a half a cup of water and reduce heat to low. Simmer until liquid is absorbed, about 10 minutes.
Divide beef between taco shells and top with tomatoes, white onion, green leaf lettuce, Mexican cheese, sour cream and hot sauce.