Prepare Stuffing: Dry roast peanuts, sesame seeds, coriander seeds, cumin seeds, and red chilies for 3–4 minutes until fragrant. Cool and grind with coconut (if using), tamarind, jaggery, salt, and turmeric into a coarse paste, adding 1–2 tbsp water.
Prepare Eggplants: Wash eggplants and make two crosswise slits from the bottom, keeping stems intact. Soak in salted water for 10 minutes, then drain and pat dry.
Stuff Eggplants: Fill each eggplant with the spice paste, reserving any extra for later.
Temper Spices: Heat oil in a wide pan over medium heat. Add mustard seeds, cumin seeds, and curry leaves; let splutter for 10 seconds.
Cook Eggplants: Place stuffed eggplants slit-side up in the pan. Cook for 2–3 minutes, flip gently, then add 1 cup water. Cover and simmer for 15–20 minutes until tender.
Finish: Cook uncovered for 5 minutes to reduce liquid if desired. Garnish with cilantro and serve hot.