In a skillet heat oil, and add the mustard seeds. When the mustard pops, add the cumin seeds and let them sizzle for 15- 20 seconds and add asafoetida.
Add the finely chopped onion, ginger, garlic and green chili and a pinch of salt.
Cook till the onion turn soft, about 5 minutes.
Add the chopped tomato, turmeric, red chili powder, coriander and cumin powder, salt and brown sugar. Give a mix and cook for 30 -35 minutes, stirring in between. do not close the lid while cooking. Mid way in the cooking, taste and adjust the salt and spices.
After 30 -35 minutes, all the moisture from the tomatoes will be absorbed and the chutney will be thick. At this point you can add some lemon juice to taste. Let it cool for few minutes.