Grind tomatoes, coconut, onion, garlic, coriander seeds, pepper corn, dry red-chilli, turmeric to a smooth paste by adding little water to it and set aside.
Heat oil in a pan.
Add mustard seeds and let it crackle.
Now add cumin seeds and let it splutter.
Now add curry leaves, dry red chilli and asafoetida and stir.
Add chopped onion and saute till it is slightly brown.
Now add tomatoes, salt and saute for 5-6 minutes.
Add ground paste and water as per required and simmer the tomato curry uncovered, stirring in between.
Let it simmer for about 15 minutes on low flame and then turn off the gas.
Garnish with coriander leaves and serve along with steamed rice and some side dish of your choice.
Notes
If you want you can add tamarind paste to get more tangy taste.