Toss the acorn squash cubes with some salt and pepper. Spray them with oil, toss to coat, and spread in a single layer on a baking sheet. Bake in a preheated 350-degree oven 30-40 minutes or until the squash is tender. Set aside.
Add the coconut milk, cumin seeds, red chillies and ginger to a blender. Blend into a smooth paste. If using grated coconut, add some water to make the paste.
Heat the coconut oil, add the onions, and saute until the edges start to just brown.
Add the turmeric, cumin powder and coriander powder. Stir to coat the onion with the spices.
Add the coconut paste and cook, stirring frequently, until a lot of the moisture has evaporated. You need to do this to ensure all of the spices are cooked.
Add the acorn squash cubes and the tomatoes. Stir to mix. Add some water if the curry is too dry.
Bring to a boil, lower the heat to a simmer, and cook, covered, for 5 minutes.
Add the sugar and mix well. Add the chopped coriander and serve hot with rice or rotis.