Prepare all the ingredients for making the sauce and set aside. Heat oil in a kadai for deep frying paneer.
While the oil heats, add corn flour, maida, salt and chilli powder to a bowl. Add water just enough to make a free flowing yet thick batter. The consistency must be moderately thick, not too thick or too runny.
Test if the oil is hot by dropping a small portion of the batter to the oil. It should immediately sizzle and come up to the surface without turning brown. This is the right temperature.
Dip the paneer cubes in the batter and gently drop to the hot oil. Do not disturb them for a minute or 2 until the coating set firmly over the paneer.
Stir often and fry on a medium heat until golden and crisp. Remove them to a steel colander.
To a mixing bowl add 1 tablespoon soya sauce, 2 teaspoons ketchup (tomato sauce), little sugar and mix well. Add paneer and give a good stir.
To a small bowl, add 1 tablespoon corn starch, 1 tablespoon all-purpose flour and 2 to 3 pinches of black pepper. Mix together and sprinkle all over the paneer.
Coat the paneer well with the flour. If the mixture is too dry, sprinkle little water. Each piece of paneer should be well coated with a thick batter.
Heat a tablespoon of oil in a non-stick pan. When the oil turns hot, place each piece in the oil, each atleast an inch apart. Fry until crisp on both the sides, turning to the other after one side turns golden.
To air fry, place them on a sheet and air fry for 6 to 8 mins at 350 F or 180 C, turn the pieces and air fry for another 5 mins.
Add 1 teaspoon corn starch to a bowl and add ½ cup water. Mix and make a lump free slurry. Keep this aside.
Heat 1 tbsp of oil in a wok. Regulate the flame to high. Add ginger garlic and saute for a min for the nice aroma to comes out.
Next add spring onion whites and fry for a min or two. Add capsicum and saute for another minute.
Pour soya sauce, tomato sauce and corn slurry. Make sure you stir the corn slurry once before pouring to the pan.
Add more water if needed. Reduce the flame to medium and add sugar. Stir and check the taste test.
Add black pepper, salt and vinegar if needed. Let the sauce boil and cook down to a thick consistency.
Add the fried paneer and spring onion greens. Toss the paneer in the sauce well to coat evenly.
Serve paneer manchurian hot with noodles or fried rice.