Use a heavy knife to cut the squash in half from the stem to the end of the squash. Use a spoon to scoop out and discard the seeds and the stringy bits from the squash.
Place the squash cut side down in a microwave-safe baking dish. Add 1/2 cup water to the dish and microwave the squash for 15 to 20 minutes. The squash will be done when you can easily pierce it with a fork.
Set your oven to broil.
In the microwave or on the stovetop, melt the butter and stir in the brown sugar, pumpkin pie spice, and salt. Place the microwaved squash in an ovenproof dish, and drizzle the butter over the squash.
Broil for 5 to 7 minutes. The butter will begin to bubble and the brown sugar will begin to caramelize. Serve immediately.