Prepare the pumpkin. You may peel off the skin or keep it (in that case, make sure that skins are edible). Dice into 1.5 inch pieces.
For reference, I use 3 qt Instant Pot for making this curry. Plug in the instant pot. Press saute and set the timer to 15 minutes.
Add oil and let heat up. Add the mustard seeds, fennel seeds & the dried chillies. Wait for the spices to crackle. If they don't pop, mustard seeds will taste bitter.
Immediately add the chopped ginger and garlic. Fry for 8-10 seconds, taking care that they do not burn. Tip :- Ginger and garlic burn pretty quickly, and that will change the taste of your curry. Add a tablespoon or two or water to bring the temperature down. Next goes in the chopped onions. Fry the onins for 5-6 minutes or until they start turning golden brown. If your IP shows hot or burn, add a tablespoon or two or water to bring the temperature down.
Sprinkle the spice powders (except garam masala) and add the curry leaves. Fry for 5-6 seconds.
Add the chopped tomatoes next. Cook for 1-2 minutes and the tomatoes will start turning soft.At this point, also add ¼ cup hot water and fry the tomatoes till you see oil seperating.Tip - Add ¼ teaspoon of sugar right now if you like a sweetish profile in your curry. Introduce the pumpkin, sprinkle salt. Stir to coat the pumkin in the masala and fry for 2 minutes.
Next, add garam masala and ¾ cup water, just enough to soak the pumpkin cubes. Press the cancel button.
Press pressure cook on "normal" and set timer for 2 (or 3) minutes with vent in seal position. Let pressure release naturally for 3 minutes and then release the pressure manually.
Open the lid, you will see that the curry is hot and bubbling. Wait for it to come to a simmer (2-4 minutes). Don't stir else hot pumpkin will get mushy.
Add in the coconut milk, garam masala and lemon juice. Simmer the curry for 1-2 minutes on saute mode taking utmost care that coconut milk does not boil. Dont stir the curry else the pupmkin will break,the coocnut milk will mix on its own as curry simmers.
Garnish with chopped fresh coriander leaves and serve warm.