Pour Knorr liquid seasoning and oyster sauce over the beef sliced. Add the ground black pepper. Mix well.
Add the cornstarch. Mix until all the ingredients are distributed. Let is stay for 5 minutes.
Heat 3 tablespoons oil in a pan.
Stir-fry the bell peppers for 3 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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