Using a vegetable peeler, peel some of the tough skin off drumsticks. Cut off the ends and then cut drumsticks into 3-inch lengths.
Heat vegetable oil in a medium sized pot. Fry onions, garlic, curry leaves, cumin, and mustard seeds in hot oil until fragrant and lightly browned, about 3 minutes.
Add curry powder and continue to stir for another 2 minutes.
Pour in water and allow it to come to a boil.
Stir in tamarind paste and season with salt.
Add drumsticks and tomatoes. When it comes back to a boil, reduce heat and allow it to simmer for 10 minutes.
Finally, add shrimp and allow it to cook for another 3 minutes or until shrimps curl and turn pink.
Remove and serve with steamed rice.