1. Cut each eggplant in half lengthwise without cutting through the stem. Roll each one over and cut lengthwise again, still keeping the stem intact. Place in a bowl of cold water and set aside.
2. Put a large lidded frying pan over medium heat. When hot, toast the coconut and peanuts for 2 to 3 minutes, until the coconut begins to brown. Pour into a bowl and let cool. Put the coriander, garlic, green chili, tomato puree, cumin, turmeric, sugar, and salt into a food processor along with the cooled peanuts and coconut. Pulse until coarsely ground and fully mixed.
3. Open each eggplant like a flower and fill with the coconut mixture. Roll the eggplant over, open, and stuff again, then press closed. If there's any leftover stuffing, add it to the pan when you cook the eggplants.
4. Next, put the oil into the frying pan over medium heat. When hot, add the onion and fry until golden and soft. Add the eggplants and 2 tablespoons of water, turn up the heat, and cook for a few minutes. Then, put the lid on and reduce heat. Cook for 10 minutes. Gently turn the eggplants and add water if they appear dry. Cook for an additional 20 minutes or until tender. Serve with a cucumber and mint raita, or with a salad, yogurt, and rice or chapattis.