Add 2 tablespoon of olive oil in the pan in medium heat. Once it is hot, add onion and stir it for a minute or until it is light brown.
Add the marinated liver along with the sauces on the pan, and quickly stir them for 10 second. Cover the pan from any utensils and let it cook for 6 to 10 minutes.
Once there is few juices left, add 1 tablespoon of olive oil and chopped bell pepper, and quickly stir for few seconds.
Add oyster sauce, soy sauce, salt and black pepper in the pan. Mix them well to make sure the sauce and the seasoning are well distributed with the liver. Turn off the heat, and garnished with chopped parsley.
Notes
Do not over stir the chicken liver during cooking since it may break into pieces
If you don’t have olive oil, you can use any vegetable oils.