Peel the ridge gourd and cut it into small, bite-sized pieces, roughly 1 inch (2 ½ cm.) in size.
Heat the oil over medium heat in a large pan. After 90 second, when the oil is hot, stir fry the mustard seeds and cumin seeds, allowing them to sizzle and pop for a few seconds.
Stir in the Kashmiri red chili powder, turmeric, asafetida, dried kasoori methi, minced green chilies, and curry leaves. Stir and cook for just 1-2 minutes until fragrant.
Add the chopped ridge gourd to the pan and stir to coat it with the spice mixture. Add the shredded coconut, water, cilantro and salt, then cover the pan and cook over very low heat for 7-10 minutes, or until the ridge gourd is just tender.
To prepare the tadka, heat the oil over medium-high heat in a small pan. After 90 seconds, when the oil is hot, stir in the curry leaves, dried chilies, kalonji seeds, sesame seeds, asafetida, and salt. Cook for 1-2 minutes, stirring continuously until the seeds are fragrant and slightly toasted.
Transfer the cooked ridge gourd sabji into an attractive serving dish and top it with the tadka. Garnish with fresh cilantro leaves and strips of green chili before serving.