Preheat the oven to 415 degrees F. Trim the top off of the kabocha squash, cut it in half, and scoop out the seeds. Drizzle the flesh with olive oil, sprinkle with salt, and place cut-side down on a baking sheet. Roast for 55 to 65 minutes until very soft. Scoop the flesh into a bowl to cool.

Once cool, add the kabocha squash to a high-powered blender with the filling ingredients and blend until well combined. Alternatively, use a potato masher and mixing bowl. Transfer the mixture to a 9-inch round casserole dish or a 13" x 9" baking dish and preheat the oven to 375 degrees F.

Stir together the topping ingredients until well combined. Evenly spread the topping over the kabocha squash filling.

Cover the casserole with aluminum foil and bake at 375 degrees for 20 minutes. Remove the foil and bake for another 20-30 minutes, or until the topping is golden brown and the filling is bubbly. Cool for 15 minutes before serving.