Heat cooking oil in a wide saucepan and fry chopped garlic. Once the garlic changes color slightly, add the chopped onion with some white portion of spring onion and chopped green chili. Fry for a few seconds and then add chopped capsicum, soy sauce, red chili sauce, tomato sauce, brown sugar, red chili powder, and white vinegar. Cook on low flame for 2 minutes while constantly stirring.