In a bowl, coat the cubed tofu with cornflour and a pinch of salt.
Heat oil in a pan and fry the tofu until golden brown. Remove and set aside.
In the same pan, add chopped onion, capsicum, and green chillies. Sauté until soft.
Add ginger-garlic paste and sauté for another minute.
Mix in soy sauce, vinegar, tomato ketchup, red chilli powder, and salt. Stir well.
Add the fried tofu and water, and cook for 5 minutes until the sauce thickens.
Garnish with chopped coriander leaves and serve hot.