Slice steak, across the grain, into 1/4 inch thick strips, and place in a large plastic bag.
Add soy sauce and massage into the meat. Add cornstarch and 5 spice, seal the bag and toss/massage to coat the meat.
Let meat marinate for about 10 minutes or so.
In a medium mixing bowl, whisk together sauce ingredients and set aside.
Slice vegetables and set aside.
Add sesame oil to wok (or large sauté pan) and heat over MED-HIGH heat.
Add beef to hot pan (just enough to cover the bottom of the pan - you'll probably want to do at least 2 batches), and sauté about 2-3 minutes. Remove beef to a plate and cook remaining batches.
Add sliced vegetables to the hot pan and cook about 1-3 minutes (depending on how tender you want them), stirring often.
Pour in Szechuan sauce and cook about a minute, until slightly thickened.
Add cooked beef and turn to coat in the sauce.
Serve over basmati rice.