This is a quick-cooking dish so you'll need a tender cut of beef. Definitely not brisket or anything that requires long and slow cooking. The beef should be sliced thinly, no more than an eighth of an inch, and you'll want to cut the thin sliced into strips.If you're wondering what "quick-cooking" means, it means cooking the beef with the softened onion slices together just long enough to soak up the seasonings. That means about ten minutes plus another five to soften the onion slices in hot oil.