Heat vegetable oil in a large skillet over medium-high heat.

Add the sliced steak and cook until browned and cooked through, about 5-7 minutes.

Add the sliced bell peppers, onion, and garlic to the skillet. Cook for another 3-5 minutes until vegetables are tender-crisp.

Stir in the soy sauce and oyster sauce, mixing well to coat everything evenly.

Season with salt and pepper to taste.

Serve hot, garnished with green onions if desired.