Rinse the shrimp and blot them dry with a paper towel. Butter slashed the shrimp that allows more area on surface to the sauce stick on shrimp, season by dash of salt and white pepper.
1 tablespoon vegetable oil is added to a large skillet or wok and heated over medium-high. Shrimps are added, and the shrimp are stir-fried until they turn pinkish red and slightly translucent. Stir-fry for another 1–2 minutes on each side. Set aside.
Add more oil if needed. Stir-fry the chopped onions and bell pepper a little soft until about 2 minutes, adding the minced garlic and carry on another 30 seconds over medium heat till fragrant.
In a separate bowl, mix the vinegar, tomato ketchup, oyster sauce, soy sauce and sesame oil. In another bowl, whisk the water with the cornstarch to form a slurry.
Return the cooked shrimp to the pan, add the sauce, and mix until fully coated. Gradually stir in the cornstarch slurry, letting the sauce thicken as it simmers for 1-2 minutes until glossy.
Turn off the gas and sprinkle with fresh-cut spring onions and parsley. Serve immediately over steamed rice or stir-fried noodles.