Cut the cauliflower into small florets and wash them thoroughly. Drain the water, pat dry the cauliflower on kitchen paper.
In a large mixing bowl, combine cornflour, all-purpose flour, ginger-garlic paste, red chili powder, and salt (follow the proportions mentioned in the ingredient list above).
Add water little by little to make a thick batter. Using a whisk, beat the batter to add air, the batter should be thick enough to coat the back of a spoon.
Dip the cauliflower floret in the batter, and mix them until they are well coated in the batter.
Heat oil in a pan for deep-frying. Once the oil is hot, test it by dipping a drop of batter in the hot oil. The batter should rise to the top.
Then dip the battered cauliflower - a few at a time, and fry until golden brown. Do not crowd the pan. Remove from the oil and set aside.
Increase the heat to high and wait for the oil to get very hot. Drop the fried cauliflower florets again into the hot oil and fry them for a few seconds until they turn crispy and golden brown. This double frying will make the cauliflower extra crispy.
To make the sauce, heat oil in a pan and add ginger-garlic paste. Saute for a few seconds.
Add chopped onion, the chopped-up white part of the spring onions and bell pepper. Saute until the onion turns translucent.
Add soy sauce, tomato ketchup, chili sauce, salt, black pepper powder, cornflour slurry and water. Mix well and cook until the sauce thickens.
Optionally, you can add 1/2 teaspoon garam masala and chopped coriander leaves to the sauce for added flavor.
Add the fried cauliflower florets to the sauce and mix well until the florets are coated with the sauce. Garnish with chopped up green onion.
Serve hot as a snack or as a side dish with rice or noodles.