Prepare the sauce before stir frying. Mix soy sauce, sugar, oyster sauce, cornstarch and water. Make sure that the corn starch is mixed in and there are no clumps.
Make Stir-Fry
Prepare the stir fry ingredients. Chop onion, celery and bell pepper. Set these ingredients aside and prepare for the stir-fry.
Heat pan or wok on high heat. After the pan is hot (see smoke), add 1 tablespoon oil. Then add your marinated chicken and fry until golden brown and make sure the chicken is cooked through (takes 3-4 minutes). Cover the pan when the chicken is cooking to prevent oil splatter. After chicken is golden brown, take the chicken out of the pan and set aside.
The pan should still be hot (on med-high heat) and have some leftover oil from the chicken. Add an additional 1 tbs oil to the pan. Fry the red chilis, chopped onion, garlic, and ginger until the red chilis turn dark red (1 minute). Keep mixing the ingredients to ensure the garlic doesn't burn. Next, add celery and bell pepper, then stir fry the veggies for 2 minutes.
Add sauce, which helps soften the veggies. Stir well and cook for one minute. Give a good stir to the sauce (from step 3) and add to the pan. Mix together.
After the sauce starts to thicken, add the peanuts and stir. Then turn off the heat.
Serve on a plate with some jasmine rice and top with some more peanuts if you like. Hope you enjoy!