Rinse and chop onions, tomatoes and ginger. Pat dry the rinsed curry leaves. Slit the green chili.
Cut off both ends of the lauki and peel it. Chop to ½ inch pieces and keep aside.
Heat oil in a pan and add cumin seeds. When they begin to sizzle add curry leaves, followed by onions, ginger and green chili.
Saute onions on a medium heat until transparent, for about 4 to 5 mins. Add tomatoes and half of the salt. Saute until the tomatoes turn mushy, for about 3 to 4 minutes.
Stir in the red chili powder, turmeric and coriander powder if using. Saute for a minute.
Add the lauki and the rest of the salt. Stir fry on a medium high heat for 3 to 4 minutes. Pour water and give a good stir.
Cover and cook on a medium heat until lauki is soft and fully cooked. Add more water as you cook if required.
When the lauki is cooked, taste test and add more salt if required. For more flavor you may sprinkle garam masala and fennel seeds powder at this stage.
If the sabzi has lot of water, you may evaporate by cooking uncovered, on a high heat. Turn off and garnish with coriander leaves.
Serve Lauki sabzi with rice, roti, bhakri or chapati.