Slice steak into thin, 3" long strips. In a large bowl mix together cornstarch and water until completely combined. Toss the steak in the in the mixture until it is fully coated and set aside.
In a large skillet heat olive oil over a medium heat. Add in the steak and allow to fry for 4 or 5 minutes, until it is no longer pink. Remove from the skillet and set aside.
Add garlic, broccoli, onion, bell pepper, and mushrooms into the same skillet. Sauté for 3 to 4 minutes and add steak back in.
In a small bowl whisk together all the sauce ingredients and pour it into the skillet. Allow to cook for another 4 to 5 minutes.
Serve over rice or noodles ( I used some unflavored ramen lol).