With a sharp knife, slice the pumpkin in half and then again into quarters. Scoop out the seeds and use a peeler to carefully remove all of the skin. Slice the pumpkin into pieces that are 2-3 inches in size.
In a small bowl, combine the sugar, cinnamon and coriander.
Preheat the oven to 350 degrees F. Heat the oil in a Dutch oven or heavy bottom skillet over medium-high heat. Brown the pumpkin well on both sides for 5-10 minutes.
Remove the Dutch oven from the heat and sprinkle the spice mixture evenly over the pumpkin. Cover tightly and bake for 30 minutes.
To prepare the sauce, combine the yogurt and garlic. Add salt to taste. Milk or water can be added to the yogurt to thin it out if necessary.
To serve, drizzle the sauce over the pumpkin. Serve warm.