Soak tamarind in 1 1/2 cup of water for 20 minutes and take the juice.
Grind sliced onion, tomato, coconut, fennel seeds into a thick paste by adding little water as possible. Now to the coconut paste add tamarind juice, chili powder, turmeric powder, salt as needed. Mix well and keep it aside.
Heat the oils in a pan. Now add the vadagam and sauté for 15 to 30 seconds.
Now add the shallot, curry leaves and sauté until the shallots turns translucent.
Now add the shrimp and sauté for a minute.
Now add the drumstick and sauté for few seconds.
Now add the tamarind coconut mixture, 1/2 cup of water. Place a lid and boil this for 10 minutes. When the oil starts to separate. Add the crushed garlic and remove the curry from the heat (stove) and serve.