Cook pumpkin, crushed garlic, crushed green chilli, turmeric powder, cumin powder, salt and a little water in a pressure cooker for 2 whistles (around 8 - 10 minutes) or until the pumpkin is soft.
After releasing pressure, open the cooker. If you think it is too watery, leave it on low to medium flame a little longer until the gravy reduces.
Mash/puree the cooked pumpkin mixture. You can either roughly mash it using the back of a spoon or make it smoother using a blender. I like it smooth and use an immersion blender.
Add coconut milk and simmer on low flame till it just starts boiling and you see a bubble or two. Switch the flame off.
For tempering, heat oil in a small pan or wok and add mustard seeds. When the mustard starts spluttering, throw in curry leaves, shallots, dried chilli and grated/dessicated coconut. Keep stirring.
As soon as the coconut turns golden brown, switch the flame off. Immediately, add red chilli powder and mix well.
Transfer to the vessel with the mashed or pureed pumpkin mixture. Mix well.
Serve with rice. A dollop of ghee over the curry and papadom / papad are great accompaniments.