Place the acorn squash halves in a microwave-safe dish and cover with plastic wrap. Microwave on HIGH until the flesh is tender, 5 to 7 minutes.
Using a spoon or ice cream scoop, remove the flesh from the squash and transfer to a large bowl. Add the sour cream, cumin, and garlic powder and mash together with a fork until blended and smooth, adding more sour cream, as necessary, to create a nice consistency. Season with salt and pepper.
Spoon the squash onto plates and top with sunflower seeds just before serving.