Add oil to a pot or pan. When the oil is hot enough add mustard seed, fennel seed, cumin seed, and fenugreek seed. Wait until it splutters.
Meanwhile, grind the coconut into a smooth paste with the required water.
Add onion, garlic and fry till it cooks well.
Then add chopped tomato and season with salt to cook the tomato faster.
Add drumstick and mango. Saute for a while.
Add coriander powder, turmeric powder, fish curry powder and mix them in low-heat.
Add enough water and cook covered in medium heat until the vegetables are cooked.
Now add sardines along with the coconut paste and cook covered.
Check the saltiness in this stage, and add if required.
Add curry leaves and serve hot with white rice, Black gram rice, Idli, Dosa, Chappathi, and Appam.