NOTE: If you are going to make rice to accompany this, start the rice before adding anything to the wok. You want the rice to be done before or at the same time as everything else. Letting the stir fry sit can cause the veggies to wilt, the beef to toughen and the sauce to thin (if covered). I use Minute Rice and start it before I pull out the wok.
Combine oyster sauce, soy sauce, beef broth, sugar and cornstarch and set aside.
Heat 1 tbsp oil in wok on high heat. Add ginger and stir fry 10 seconds, add garlic and stir fry another ten seconds. Add the beef and stir fry quickly, until no longer pink, hopefully no longer than 4-5 minutes. Remove beef and keep warm.
Add 1/2 tablespoon of oil and heat on high. Add green pepper and onion and stir fry for 2-3 minutes. Add tomatoes and stir fry for 1-2 minutes. Move vegetables to one side of the wok and add the beef on the other side of the wok. Pour the reserved sauce into the center and stir a little, allowing it to thicken a bit, 2-3 minutes.
Combine beef, vegetables and sauce and toss to coat. Serve over rice.