Heat oil in a big saucepan. Splutter the mustard seeds and briefly fry the fenugreek seeds. Let the hing also fry.
Add in tomatoes with some salt and give it a good toss.
Get it cooking on low flame, stirring it occasionally. The tomato will start releasing its fluids and then slowly start drying up.
Add in the powders and give it a good stir. Continue to cook till the tomatoes are fully mashed and the mixture is almost dry. Adjust the seasoning by adding sugar and salt.
Switch off and cool completely before storing it in a sterilized bottle.
Notes
If you wish, you can add one onion, minced in the beginning before adding the tomatoes. Rest all process is the same.