In a pan, add oil and fry the onion till translucent.
Now add the green chili, garlic, tomato, salt, turmeric and cook till the tomato pieces are tender.
Throw in the diced bottle gourd / lauki, red chili powder and water and cook till it is cooked. (You can alternatively cook it in a pressure cooker to save time. Just 1 or 2 whistles of the pressure cooker will be sufficient to cook the bottle gourd thoroughly)
Add a cup of water, coconut paste, tamarind paste and coriander leaves, cook on low flame till oil begins to float on top.
Serve hot with steamed plain rice