In a dry frying pan, toast the mung beans over medium-high heat, stirring constantly until they begin to brown. Remove them to a strainer or fine colander and wash them briefly under running water; drain. Place the beans in a saucepan with 3 cups water and bring to a boil. Cover, reduce the heat to low, and simmer 20 minutes or until just tender.
Peel the pumpkin and remove the seeds. Cut into 3/4-inch cubes and measure 8 cups. Set aside. Put 1 1/2 cups coconut, the garlic, and the ground masala in a blender or food processor. Add 1 cup water or more and process the mixture to the consistency of thick pesto. Set aside.
In a wide deep pan combine the pumpkin, turmeric, cayenne, salt, and 3 cups water. Bring to a boil, reduce the heat, and simmer, covered, until the pumpkin is tender and begins to break up when stirred (20 to 25 minutes). Add the cooked mung beans and the coconut paste and stir to combine. Bring to a boil, then remove from the heat.
In a frying pan, heat the oil over medium-high heat. Add the mustard seeds and cover. When the seeds pop, toss in the dried red chilies and fry for a few seconds. Add 1/4 cup of coconut and stir constantly over medium-high heat until the coconut turns cinnamon-brown and no white remains. Stir this into the cooked vegetables and heat the mixture until warmed through, adding more water if it dries out. Remove from the heat and check the salt. The curry should appear as chunks of pumpkin with a thick sauce.