Cook the beef and onions until beef is no longer pink, drain off the fat. Srir in picante sauce and water, green chilis and seasoning mix cook over low heat for 5 minutes.
In a 13' by 9' baking dish layer half of the broken taco shells on the bottom of the dish, Cover with half of the of the meat mixture , sprinkle with one cup of cheese. Repeat with the remaining meat mixture and taco shells and cheese.
Bake for 25 minutes or until hot and bubbley.
Let stand 5 minutes then top with green onions, chopped tomatoes and sour cream ,add more broken taco shells on top and serve.