Prepare the lauki: Rinse the lauki thoroughly, peel the skin lightly (do not peel too deep), then cut it in half lengthwise. Slice each half into ½-inch strips, then cut into small cubes or pieces. Smaller pieces cook more evenly and help the lauki soften and break down properly.
Heat oil (medium heat): Add the oil to a pot and heat until warm but not smoking.
Add panch phoron (medium heat): Sprinkle in the panch phoron first and cook for about 30 seconds, allowing the seeds to toast and release their aroma.
Cook aromatics (medium heat): Add the chopped onion, sliced hot pepper, and curry leaves. Cook for 3–5 minutes until the onion softens and the edges of the onion and hot pepper begin to brown. This step builds the base flavor of the dish.
Add turmeric and garlic: Add the turmeric (if using) and the pounded or minced garlic. Stir and cook for about 30 seconds, just until fragrant, being careful not to let the garlic burn.
Add lauki and season: Add the chopped lauki, chopped tomatoes (if using), culantro (or scallions), and salt. Stir well to combine and coat the lauki with the seasonings.
Cover and cook (medium-low heat): Cover the pot and cook for 20–30 minutes, stirring occasionally to prevent sticking.
Use lid moisture: Each time you remove the lid, pour the liquid collected on the underside of the lid back into the pot to support the steaming process.
Cook until tender: Allow the lauki to release its natural liquid and soften until tender. It should be soft and delicate; note that some lauki may remain slightly firm depending on freshness.
Finish and adjust: Taste and adjust salt if needed. Serve warm.