Dont skip spring onions as it gives a nice flavour.
Refrigerating idlis helps in giving firm idli cubes with no crumbles.
Soya sauce forms the base for any manchurian.You can even use green chilli sauce / red chilli sauce.
The consistency is purely your choice, you can make it saucy like how I have did or make it dry too.
Always serve hot as it may turn soggy when rested for a while.
Adding cornflour water mixture is purely optional - this is just to make the sauce thick.
Don't add more soya sauce than the mentioned amount else it will change the taste and make the manchurian more darker in color.
After the fried idlis are added just toss it, that's enough.