Heat oil in a heavy-bottomed pan over medium heat. Add mustard seeds and cumin seeds, allowing them to splutter. Add curry leaves.
Add finely chopped onion and slit green chili to the pan. Sauté until onion turns golden brown.
Add chopped eggplant along with turmeric powder, Kashmiri red chili powder, garam masala, and salt. Mix well and sauté for 5-7 minutes.
Add tomatoes and cook until they become soft and break down completely, about 5 minutes.
Pour in water, bring to a boil, then reduce heat and simmer covered until eggplant becomes tender, approximately 10-12 minutes.
Stir in fresh coriander leaves and serve hot.