Marinate the fish with lime juice, salt and pepper powder and keep aside for 30 minutes.
Heat oil in a pan and shallow-fry them till golden brown on either side.
Drain onto an absorbent paper and keep aside.
Strain the oil and keep aside for further use.
Heat 3 tablespoons of the strained oil in a pan.
Add the chopped onion, garlic and ginger and saute for 10 seconds on high heat.
Add the chilli paste (or 1-1/2 tbsps of Kashmiri Chili powder mixed in water), ajinomotto (if using), soy sauce and vinegar and mix well.
Add the water and adjust the seasoning.
Bring the mixture to a boil.
Drop the fried fish into it and cook till the gravy starts to boil.
Add the cornflour mixture and stir well.
When the gravy thickens to your requirement, switch off heat and transfer to a serving plate.
Garnish with chopped spring onion and serve with Rice or Noodles.