Do I need to cut open a summer squash before baking it?

Cut it up--the flesh will be exposed to the heat and caramelize a bit, which will make it sweeter and firmer. If you have a hard time cutting, slice it just above the bulbous end. Slice off the stem end and then cut the solid piece into thick slices. Then place the cut butternut flat on a cutting board and slice off the skin. You can handle the bulb in a similar manner, although it is easier if you slice the bulb in half lengthwise and then slice it as above.

Oops, I mean butternut squash!!

No, you can bake it whole. You'll like this article http://www.thekitchn.com/quick-tip-an-ea-159575