Heat vegetable oil in a wok or large cooking pot. Add chopped vegetables and saute on high flame for 5-6 minutes. The vegetables should be cooked but remain crunchy.
Take out the vegetables on a plate and keep them aside.
In a bowl, mix soy sauce, chili sauce, vinegar, and brown sugar. Keep the sauce mix aside.
Heat sesame oil in a wok. Add chopped garlic, ginger, the white part of spring onion, and dried red chilies. Saute for about a minute.
Add diced onion and saute until it becomes translucent.
Add chili flakes and saute for a few seconds.
Next, add the sauce mix and cook for about 30 seconds.
Add water and let it boil.
While the sauce is boiling, mix corn starch and some water in a small bowl. Add this corn starch slurry to the boiling sauce.
Stir continuously and cook until the sauce thickens.
Add sauteed vegetables and mix. Cook for about 1 -2 minutes and then switch off the stove.
Garnish with chopped spring onion greens.