Wash 500 grams of small brinjals and slit them lengthwise, keeping the stem intact. Set aside.
In a pan, dry roast 2 tablespoons of coriander seeds, 1 tablespoon of cumin seeds, 1 tablespoon of fennel seeds, and 1 tablespoon of sesame seeds until fragrant. Let it cool and then grind into a coarse powder.
In a bowl, mix the ground spice mixture with 1 tablespoon of red chili powder, 1/2 tablespoon of turmeric powder, 1/2 tablespoon of amchur (dry mango powder), and salt to taste.
Stuff the brinjals with the prepared spice mixture, ensuring that the mixture fills the slits well.
In a kadai or heavy-bottomed pan, heat 2 tablespoons of oil. Add 1 teaspoon of mustard seeds and let them splutter.
Add the stuffed brinjals to the pan and cook on medium heat for 5 minutes, turning occasionally to ensure even cooking.
Add any remaining spice mixture to the pan along with 1/2 cup of water. Cover and cook on low heat for 15-20 minutes, or until the brinjals are tender and cooked through.
Garnish with chopped coriander leaves and serve hot with roti or rice.