Preheat the oven to 350°.
Preheat a thick-bottomed pot on medium heat, adding the oil once it's warm. Dice the onion and sauté until translucent. Turn down to medium low.
Mince garlic and chilis, if using. Grate ginger, wash and chop cilantro stems. Sauté everything together on medium low.
Peel and seed the pumpkins, or whatever squash you have. A thinner skinned squash willl yield more flesh, so you could start with 3½-4 lbs. Chop into roughly evenly sized cubes and add to the pot.
Add water just to cover, then add coconut milk and 2 tsp of salt.
Chop lemongrass and wrap in cheesecloth or put into a dispoable tea bag and add to soup. Add lime leaves and salt.
Bring to a boil then turn heat down and simmer until pumpkin is soft, about 15-20 minutes. Let cool a bit.
Rinse seeds, discarding most of the stringy flesh. Don't worry if you don't get it all, it will dry up and separate more easily after baking. Cover seeds in 1 tbsp of oil and 1 tsp of salt.
Spread on a parchment-lined rimmed cookie sheet. Toast for 15-20 minutes, stirring halfway through. Toast until golden brown.
Come back to your soup. Just before you pour it in the blender, remove the lemongrass and lime leaves. Fill the blender no more than 2/3 full, and make sure there's a little ventilation if it's still steaming hot. You do not want your kitchen to look like a Jackson Pollack painintg.
Blend until silky smooth. Pour back into the pot to reheat before serving. Top with cilantro, pumpkin seeds, and unsweetened toasted coconut, if you have it. Voilà!