Gather all the ingredients for cooking.
Finely chop onions and tomatoes. You may use hand chopper as it is really easy to use and quick.
Take a pan or kadhai over high heat and add oil into it.
Once oil is hot, tip in mustard seeds and it will start to splutter in hot oil. Also, add cumin seeds into the pan and let it crackle for couple of seconds.
Turn heat to medium and tip chopped onions into the pan. Stir well until onions starts changing its colour.
Next add ginger and garlic paste into the pan. Mix everything well and cook over medium heat for another 2-3 minutes.
Add powdered spices like turmeric, red chilli, coriander powders along with salt.
Give a quick stir to combine everything. You may add little hot water if mixture is too dry.
Fry over medium heat until raw smell of spices goes away and everything is well combined.
Next goes chopped tomatoes into the pan. And mix everything together.
Tomato has its own moisture; but if required add 1/4 cup of water.
Add garam masala powder along with sugar and give a quick stir. Let it cook over medium heat for 5-7 minutes.
Once tomatoes are cooked, it changes its colour and water will evaporate.
Tip in chopped coriander and mix it well.
Simmer for another 4-5 minutes. Tomato chutney or Tomato-onion sabji is ready to serve.