Microwaving the uncut squash for 1-2 minutes on high makes it easier to slice. Use a large, well-sharpened knife when cutting the squash. If it is large, cut the squash in half at the neck and cut the large bottom bulb in half lengthwise to make half moons instead of full slices.
Using a parchment-lined sheet pan saves time on clean-up. (I didn't for this batch, but often do when roasting vegetables.)
The top side does not look cooked halfway through the cooking. Once you turn the lsices over, you'll see that the bottom side has browned and the edges are nicely caramelized.