Use a heavy knife and cut the squash in half from the stem the end of the squash. Use a spoon to scoop out the seeds and the stringy bits from the squash. Discard the seeds and stringy bits. Place the squash cut side down in a microwave-safe baking dish.
Add 1/2 cup of water to the dish and then microwave the squash for 15 to 20 minutes. The squash will be done when you can pierce the fruit with a fork. The fork should pierce the squash easily.
Place your oven on broil. Melt the butter and stir in brown sugar, pumpkin pie spice, and salt. When the squash has cooked in the microwave place the squash on an ovenproof dish, and drizzle butter sauce over the squash.
Place the squash under the broiler and broil for 5 to 7 minutes, the butter will begin to bubble and the brown sugar will begin to caramelize. Serve immediately.