Heat two tablespoons sesame oil in a very large skillet over medium-high heat.
Season beef generously with salt and pepper.
Add beef and stir-fry, cooking meat until cooked through—about 5 minutes.
Remove beef from heat and set on paper-towel-lined plate.
Set aside.
Add remaining 2 tablespoons oil to skillet.
Then add frozen vegetables, green onions, bell pepper, garlic and ginger.
Stir-fry veggies until tender, about 3-5 minutes.
Push vegetables to the side of the skillet and add beaten eggs.
Scramble eggs then break into pieces while scrambling.
Stir in to remaining veggie mixture.
Add cooked beef, cold, cooked rice, Tamari soy sauce and oyster sauce, if you’re using it.
Stir well to combine ingredients.
Season with additional salt and pepper, if desired.
Garnish with green onions to serve.