In a bowl, marinate beef with oyster sauce, seasoning, pepper and cornstarch. Mix well and set aside.
Heat 3 tablespoons oil in a pan.
Stir-fry the bell peppers for 3-5 minutes.
Remove the bell peppers and set aside.
Add 1 to 2 tablespoons of oil in the same cooking pot. Add the marinated beef. Stir fry for 8 minutes or until the beef is completely cooked.
Add the bell peppers back and then stir-in the scallions. Stir-fry for 3 minutes.
Transfer to a serving plate. Serve over rice.
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