Get out and measure all of your ingredients.
In a cup mix oyster sauce, ⅓ cup water, cornstarch, salt, and pepper.
Stir until incorporated and set aside.
In a large skillet, on medium high heat, place 2 tablespoons of oil until it is shimmering or when flicking a drop of water in it causes it to dance. Add sliced beef or chicken and sauté until browned and, if using chicken, it is no longer pink. Around 4 or 5 minutes. Remove meat and set aside.
Heat remaining 2 tablespoons of oil over medium high heat until it shimmers or a drop of water flicked in it dances as well. Add onions and stir for a few minutes until tender.
Then add peppers and stir for a few more minutes until tender.
Add cooked beef or chicken and oyster sauce mixture.
Stir to coat and thicken sauce, just a few minutes.
Serve with rice or noodles. Enjoy!