Rinse the long brinjal under tap water and cut them in to 1" long pieces. Soak them in enough water to avoid discoloration.
Method
Peel off the onion and slice it in to 1" long pieces. Also chop the tomato in to big chunks. Next heat a pan and add all the ingredients under the "To temper" list. Saute till the mustard seeds splutter and include onion slices.
Continue sauteing the onions till they turn translucent. Next include tomato chunks followed by turmeric powder. After sauteing for couple of minutes, include the long brinjal pieces draining water completely.
Give a stir and let it cook with lid covered for about few minutes in low flame. If it is too dry, you can sprinkle few tea spoon of water now. Next add the salt, red chilly powder and coriander powder. Combine and cook till the brinjal is cooked soft.
Simple and easy green long brinjal curry is ready to serve with rotti and chapati.
Notes
The brinjal curry tastes yummy when cooked in oil itself. I haven't added any water, if you feel it is too dry you can sprinkle some water.
Soaking the brinjal pieces in water helps in avoiding discoloration and astringent taste of the veggie.
You can spice it up a bit with additional green chilly too.