Prep the squash by vigorously poking it with a fork a few times so air can escape. There is no need to dull your knife or cut before cooking.
You can also place the squash in a roasting pan lined with aluminum foil. Cover it with more aluminum foil to help it steam.
Smaller squash will cook more quickly than larger squash. Check the squash after 30 minutes to gauge cooking. Test with a fork—it should easily pierce the skin and squash should be tender.