Heat oil in a pan. Add sliced onion, chopped garlic, ginger, and green chillies, green onions. Sauté for a minute on high flame.
Then add chopped veggies. Sauté for 2 minutes. Add water and boil for 4 – 5 minutes till they are soft and tender. Don’t overcook vegetables.
Add soy sauce, white vinegar, and vegetable stock or water. Add salt. and a pinch of sugar to balance the flavor. Add less salt as soy sauce has some salt in it.
Let it simmer for 2 minutes. Add black pepper and salt.
In a small bowl, mix the corn starch with 2 tbsp of water and stir well to make a slurry. Add this mixture to boiling soup to give it a thicker consistency.
Season with black pepper and serve hot. Garnish with Spring onions.