Step 1

Marinate the beef. In a large bowl, combine the beef with the cornstarch, sesame oil, and soy sauce. Mix until the beef is evenly coated. Set aside and let marinate for 10 minutes.

Step 2

Make the stir fry sauce. In a small bowl, combine the cornstarch and water. Stir to dissolve the cornstarch. Then stir in the oyster sauce, soy sauce, rice vinegar, and sesame oil. Set aside.

Step 3

Cook the beef. In a large pan over high heat, add the marinated beef and cook for 2 minutes (until browned). Remove the beef from the pan when it is about 80% cooked. Set aside on a plate.

Step 4

Cook the vegetables. In the same pan over medium-high heat, add a little oil and the garlic and ginger. Saute for 2 minutes. Add the onion, green pepper, and celery. Saute for 2-3 minutes. Add the tomatoes and cook for another 2 minutes.

Step 5

Slide the beef back into the pan, cook for 1 minute. Add the green onions and cook for 1 more minute.

Step 6

Add the sauce mixture to the pan. Stir to mix and bring everything to a quick boil. All finished! Turn off the heat. Plate and serve with a big bowl of rice.