I pierce the whole squash multiple times with a knife. Then microwave it for 15 minutes. Make sure you pierce it deep enough to allow the steam to escape. When done then cut open and scoop out insides.
I usually pierce the squash 4 or 5 times and then put the whole thing in the microwave for 3 mins to soften it a little. Then, cut it in half lengthwise and remove the seeds. Place 1/2 the squash (meat side down) in a casserole dish with about an inch of water on the bottom. Microwave for 6-7 mins. Hold onto it with a towel or potholder and scrape away at the meaty part. It will come out in strings like spaghetti. If when you start trying to 'string' the squash and it isn't easy, just put it back in for a minute or two.