Marinate shrimps with vinegar, ginger-garlic paste, chilly powder, coriander powder, turmeric powder, black pepper and salt for at least 1/2 hour.
Heat oil in a pan.
Splutter mustard seeds.
Add marinated shrimps into it.
Saute for 5 mins on a medium-high flame. Stir it occasionally.
Add whole pearl onions, chopped onions, green chillies and curry leaves and saute on a medium flame for 15 mins.
Let the juice in shrimp and the onions mix with each other.
Once the onions are transparent, add coconut milk.
Boil it for 5 mins.
Add sliced tomato to the boiling curry and close with a lid.
Turn off the flame and let it stay undisturbed for at least 15 mins.
Add required salt.
:- Serve with Appam, Chappathis and Rice.
:- If the shrimp is uncooked, just marinate them and stir fry in the oil for 15 mins on medium flame and proceed to the remaining steps.